JEE Main 13 April 2023 Shift 1 question paper with solutions

JEE Main 13 April 2023 Shift 1: all 90 questions in paper order (Maths, Physics, Chemistry) with the answer key and worked solutions. Free to read; attempt it as a timed 3-hour mock test.

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Maths

Question 1

Maths · Integrals · Single correct

\[ \int_0^{\infty} \frac{6}{e^{3x}+6e^{2x}+11e^{x}+6}\,dx = \]

  1. $\log_e\left(\dfrac{32}{27}\right)$
  2. $\log_e\left(\dfrac{512}{81}\right)$
  3. $\log_e\left(\dfrac{256}{81}\right)$
  4. $\log_e\left(\dfrac{302}{27}\right)$

Answer: (a)

Solution

Let $$I = \int_0^\infty \left( \frac{6}{e^{3x} + 6e^{2x} + 11e^x + 6} \right) \, dx$$ which implies $$I = \int_0^\infty \frac{6}{(e^x + 1)(e^x + 2)(e^x + 3)} \, dx$$ Using partial fraction, we can write $$\Rightarrow I = 6 \int_0^\infty \left[ \frac{1}{2(e^x + 1)} - \frac{1}{(e^x + 2)} + \frac{1}{2(e^x + 3)} \right] \, dx$$ $$\Rightarrow I = 6 \int_0^\infty \left[ \frac{1}{2(e^x + 1)} - \frac{1}{(1 + 2e^{-x})} + \frac{1}{2(1 + 3e^{-x})} \right] e^{-x} \, dx$$ $$\Rightarrow I = 6 \left[ -\frac{1}{2} \log_e (e^{-x} + 1) + \frac{1}{2} \log_e (2e^{-x} + 1) - \frac{1}{6} \log_e (3e^{-x} + 1) \right]_0^\infty$$ $$\Rightarrow I = 6 \left[ 0 - \left\{ -\frac{1}{2} \log_e 2 + \frac{1}{2} \log_e 3 - \frac{1}{6} \log_e 4 \right\} \right]$$ $$\Rightarrow I = 3 \log_e 2 - 3 \log_e 3 + \log_e 4$$ $$\Rightarrow I = 5 \log_e 2 - 3 \log_e 3$$ $$\Rightarrow I = \log_e \left( \frac{32}{27} \right)$$

Question 2

Maths · Applications of Derivatives · Single correct

\[ \max_{0\le x\le \pi} \left\{ x-2\sin x\cos x+\frac{1}{3}\sin 3x \right\} \]

  1. $\frac{\pi + 2 - 3 \sqrt{3}}{6}$
  2. $\pi$
  3. 0
  4. $\frac{5\pi + 2 + 3 \sqrt{3}}{6}$

Answer: (d)

Question 3

Maths · Applications of Derivatives · Single correct

The set of all $a \in \mathbb{R}$ for which the equation $x|x - 1| + |x + 2| + a = 0$ has exactly one real root, is

  1. $(-7, \infty)$
  2. $(-\infty, \infty)$
  3. $(-6, -3)$
  4. $(-\infty, -3)$

Answer: (b)

Solution

Given, $x|x - 1| + |x + 2| + a = 0$. Now taking, Case I: $x < -2$, we get $$-x^2 + x - x - 2 + a = 0$$ $$\Rightarrow a = x^2 + 2$$ And $y = x^2 + 2$ is decreasing $\forall x \in (-\infty, -2)$. Now taking Case II: $-2 \leq x < 1$ we get, $$-x^2 + x + x + 2 + a = 0$$ $$\Rightarrow a = x^2 - 2x - 2$$ And $y = x^2 - 2x - 2$. So, $$\frac{dy}{dx} = 2x - 1 \leq 0 \forall x \in \left[-2, 1\right)$$ Hence, $y$ is decreasing $\forall x \in \left[-2, 1\right)$. Now taking Case III: $x \geq 1$ we get, $$x^2 - x + x + 2 + a = 0$$ $$\Rightarrow a = -(x^2 + 2)$$ And $y = -(x^2 + 2)$ is decreasing $\forall x \in \left[1, \infty\right)$. Hence, from all the cases we can say that nature of function is continuously decreasing so, it will cut $x$-axis only one time, $\therefore$ Exactly one real root $\forall a \in \mathbb{R}$.

Question 4

Maths · Mathematical Reasoning · Single correct

The negation of the statement $((A \land (B \lor C)) \Rightarrow A$ is

  1. equivalent to $\sim C$
  2. equivalent to $B \lor \sim C$
  3. a fallacy
  4. equivalent to $\sim A$

Answer: (d)

Solution

Given, $$((A \land (B \lor C)) \Rightarrow (A \lor B)) \Rightarrow A$$ We know that, $X \Rightarrow Y \equiv \sim X \lor Y$, Now using the above formula we get, $$\equiv (\sim (A \land (B \lor C)) \lor (A \lor B)) \Rightarrow A$$ $$\equiv \sim (\sim (A \land (B \lor C)) \lor (A \lor B)) \lor A$$ $$\equiv (A \land (B \lor C)) \land \sim (A \lor B) \lor A$$ Now to solve $(A \land (B \lor C)) \land \sim (A \lor B)$ let us assume a universal set $\{1, 2, 3, 4, 5, 6, 7, 8\}$, set $A = \{1, 2, 3\}$, set $B = \{3, 4, 5\}$ and set $C = \{5, 6, 7\}$ So, $A \land (B \lor C)$ will be $\{3\}$ and $\sim (A \lor B)$ will be $\{6, 7, 8\}$, So, $(A \land (B \lor C)) \land \sim (A \lor B) = \emptyset$ $$\equiv F \lor A$$ $$\equiv A$$ Therefore, negation of statement $= \sim A$

Question 5

Maths · Three Dimensional Geometry · Single correct

The distance of the point $(-1, 2, 3)$ from the plane $\vec{r} \cdot (\hat{i} - 2\hat{j} + 3\hat{k}) = 10$ parallel to the line of the shortest distance between the lines $\vec{r} = (\hat{i} - \hat{j}) + \lambda (2\hat{i} + \hat{k})$ and $\vec{r} = (2\hat{i} - \hat{j}) + \mu (\hat{i} - \hat{j} + \hat{k})$ is

  1. $4\sqrt{6}$
  2. $2\sqrt{5}$
  3. $2\sqrt{6}$
  4. $3\sqrt{5}$

Answer: (c)

Solution

The direction ratio of line parallel to the line of the shortest distance between the lines $\vec{r} = \left( \hat{i} - \hat{j} \right) + \lambda \left( 2\hat{i} + \hat{k} \right)$ and $\vec{r} = \left( 2\hat{i} - \hat{j} \right) + \mu \left( \hat{i} - \hat{j} + \hat{k} \right)$ is given by, $$\begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 2 & 0 & 1 \\ 1 & -1 & 1 \end{vmatrix} = \hat{i} - \hat{j} - 2\hat{k}$$ Now given line passing through $A(-1, 2, 3)$ And having direction ratio $(1, -1, -2)$, So, the equation is given by, $$\frac{x+1}{1} = \frac{y-2}{-1} = \frac{z-3}{-2} = \lambda$$ Let the line intersect the plane at $P$ $$P \equiv (\lambda - 1, -\lambda + 2, -2\lambda + 3)$$ $P$ lies on the plane $x - 2y + 3z = 10$ $$\therefore (\lambda - 1) - 2(-\lambda + 2) + 3(-2\lambda + 3) = 10$$ $$\Rightarrow \lambda = -2$$ Hence, point $P \equiv (-3, 4, 7)$ So, the distance of point $P(-3, 4, 7)$ from point $A(-1, 2, 3)$ will be, $$AP = \sqrt{4 + 16 + 16} = 2\sqrt{6}$$

Question 6

Maths · Probability · Single correct

A coin is biased so that the head is 3 times as likely to occur as tail. This coin is tossed until a head or three tails occur. If $X$ denotes the number of tosses of the coin, then the mean of $X$ is

  1. $\frac{38}{16}$
  2. $\frac{15}{16}$
  3. $\frac{21}{16}$
  4. $\frac{81}{64}$

Answer: (c)

Solution

It is given that $P(H) = 3P(T)$. Therefore, $P(H) = \frac{3}{4}$, $P(T) = \frac{1}{4}$. Since the coin is tossed till either $1H$ or $3T$ occurs, the process will end in the maximum of 3 throws. $$\begin{array}{|c|c|c|c|} \hline X_i & 1 & 2 & 3 \\ \hline P(X_i) & \frac{3}{4} & \frac{1}{4} \times \frac{3}{4} & \frac{1}{4} \times \frac{1}{4} \times \frac{3}{4} \\ \hline \end{array}$$ Now we know that, Mean is given by $\sum_{i=1}^{n} X_i P(X_i)$. Mean $= 1 \times \frac{3}{4} + 2 \times \frac{3}{16} + 3 \times \frac{1}{16} = \frac{21}{16}$. Hence, this is the correct option.

Question 7

Maths · Determinants · Single correct

For the system of linear equations $$2x + 4y + 2az = b$$ $$x + 2y + 3z = 4$$ $$2x + 5y + 2z = 8$$ which of the following is NOT correct?

  1. It has unique solution if $a = b = 6$
  2. It has infinitely many solutions if $a = 3, \ b = 6$
  3. It has infinitely many solutions if $a = 3, \ b = 8$
  4. It has unique solution if $a = b = 8$

Answer: (b)

Solution

Given, System of linear equations, $$2x + 4y + 2az = b$$ $$x + 2y + 3z = 4$$ $$x + 2y + 3z = 4$$ Now finding, $$\Delta = \begin{vmatrix} 2 & 4 & 2a \\ 1 & 2 & 3 \\ 2 & -5 & 2 \end{vmatrix}$$ $$\Rightarrow \Delta = -18(a - 3)$$ Hence, for $a = 3$, $\Delta = 0$ Now finding, $$\Delta_3 = \begin{vmatrix} b & 2 & 4 \\ 4 & 1 & 2 \\ 8 & 2 & -5 \end{vmatrix}$$ $$\Rightarrow \Delta_3 = 9(b - 8)$$ So, for $b = 8$, $\Delta_3 = 0$ Now solving options we get, If $a = 3$ and $b = 8$ we'll have infinite solution For $a = 8, b = 8$, $\Delta \neq 0$, $\Delta_3 = 0 \Rightarrow$ unique solution For $a = b = 6$, $\Delta \neq 0$, $\Delta_3 \neq 0 \Rightarrow$ unique solution $\therefore$ For $a = 3, b = 6$ we'll have no solution

Question 8

Maths · Relations and Functions · Single correct

For the differentiable function $f : \mathbb{R} - \{0\} \to \mathbb{R}$, let $3f(x) + 2f\left(\frac{1}{x}\right) = \frac{1}{x} - 10$, then $\left| f(3) + f'\left(\frac{1}{4}\right) \right|$ is equal to

  1. $\frac{33}{5}$
  2. 8
  3. $\frac{29}{5}$
  4. 13

Answer: (d)

Solution

Given: $$3f(x) + 2f\left(\frac{1}{x}\right) = \frac{1}{x} - 10 \ldots (1)$$ Replace $x \to \frac{1}{x}$ $$3f\left(\frac{1}{x}\right) + 2f(x) = x - 10 \ldots (2)$$ Eliminating $f\left(\frac{1}{x}\right)$ from (1) and (2), we get $$\Rightarrow 5f(x) = \frac{3}{x} - 2x - 10$$ Let us replace $x$ with 3 $$\Rightarrow 5f(3) = \frac{3}{3} - 2(3) - 10$$ $$\Rightarrow f(3) = -3$$ $$\Rightarrow 5f'(x) = \frac{-3}{x^2} - 2$$ $$\Rightarrow 5f'\left(\frac{1}{4}\right) = -48 - 2$$ $$\Rightarrow f'\left(\frac{1}{4}\right) = -10$$ $$\Rightarrow f(3) + f'\left(\frac{1}{4}\right) = 13$$ Hence this is the correct option.

Question 9

Maths · Conic Sections · Single correct

Let the tangent and normal at the point $\left(3\sqrt{3}, 1\right)$ on the ellipse $\frac{x^2}{36} + \frac{y^2}{4} = 1$ meet the $y$-axis at the points $A$ and $B$ respectively. Let the circle $C$ be drawn taking $AB$ as a diameter and the line $x = 2\sqrt{5}$ intersect $C$ at the points $P$ and $Q$. If the tangents at the points $P$ and $Q$ on the circle intersect at the point $(\alpha, \beta)$, then $\alpha^2 - \beta^2$ is equal to

  1. 61
  2. 60
  3. $\frac{304}{5}$
  4. $\frac{314}{5}$

Answer: (c)

Solution

Given that $\frac{x^2}{36} + \frac{y^2}{4} = 1$. Observe that $\left( 3\sqrt{3}, 1 \right)$ lies on the given ellipse. Equation of tangent to the ellipse at the given point is $T : \frac{3\sqrt{3}x}{12} + \frac{y}{4} = 1$. $$\Rightarrow \frac{\sqrt{3}x}{12} + \frac{y}{4} = 1$$ Equation of normal passing through same point will be $N : \frac{x - 3\sqrt{3}}{3\sqrt{3}/36} = \frac{y - 1}{1/4}$. $$\Rightarrow \frac{12x - 36\sqrt{3}}{\sqrt{3}} = 4y - 4$$ $$\Rightarrow 3x - \sqrt{3}y = \sqrt{3}y - \sqrt{3}$$ $$\Rightarrow 3x - \sqrt{3}y = 8\sqrt{3}$$ Now tangent and normal intersects the $y$-axis at $A$ and $B$ respectively. $A(0, 4)$ $B(0, -8)$. Equation of circle with $AB$ as diameter will be $$(x - x_1)(x - x_2) + (y - y_1)(y - y_2) = 0$$ $$\Rightarrow x^2 + (y - 4)(y + 8) = 0$$ Line $x = 2\sqrt{5}$ intersects the circle. $$20 + y^2 + 4y - 32 = 0$$ $$\Rightarrow y^2 + 4y - 12 = 0$$ $$\Rightarrow (y + 6)(y - 2) = 0$$ Hence $P(2\sqrt{5}, -6)$ $Q(2\sqrt{5}, 2)$. Now let us find the equation of tangents to the circle at $P, Q$. $$\Rightarrow T : xx_1 + yy_1 + 2y + 2y_1 - 32 = 0$$ $$\Rightarrow T_1 : 2\sqrt{5}x - 6y + 2y - 12 - 32 = 0$$ $$\Rightarrow 2\sqrt{5}x - 4y = 44$$ $$\Rightarrow T_1 : \sqrt{5}x - 2y = 22 \ldots \ldots \ldots (i)$$ $$\Rightarrow T_2 : 2\sqrt{5}x + 2y + 2y + 4 - 32 = 0$$ $$\Rightarrow 2\sqrt{5}x + 4y = 28$$ $$\Rightarrow T_2 : \sqrt{5}x + 2y = 14 \ldots \ldots \ldots (ii)$$ From (i) and (ii) $$\alpha = \frac{18}{\sqrt{5}} = \frac{18}{\sqrt{5}}$$ $$\Rightarrow \alpha^2 - \frac{9}{2} = \frac{304}{5}$$ Hence this is the required option.

Question 10

Maths · Applications of Integrals · Single correct

The area of the region enclosed by the curve $f(x) = \max\{\sin x, \cos x\}$, $-\pi \leq x \leq \pi$ and the $x$-axis is

  1. $2\sqrt{2}\left(\sqrt{2} + 1\right)$
  2. $4$
  3. $4\left(\sqrt{2}\right)$
  4. $2\left(\sqrt{2} + 1\right)$

Answer: (b)

Solution

Plotting the required diagram we get, Now from diagram we can say that, $\sin x$ is maximum for $x \in \left( -\pi, -\frac{3\pi}{4} \right) \cup \left( \frac{\pi}{4}, \pi \right)$ and $\cos x$ is maximum for $x \in \left( -\frac{3\pi}{4}, -\frac{\pi}{2} \right) \cup \left( -\frac{\pi}{2}, \frac{\pi}{4} \right)$. So, area of the region is given by, $$A = \left| \int_{-\pi}^{-\frac{3\pi}{4}} \sin x \, dx \right| + \left| \int_{\frac{\pi}{4}}^{\pi} \sin x \, dx \right| + \left| \int_{-\frac{\pi}{2}}^{-\frac{3\pi}{4}} \cos x \, dx \right| + \left| \int_{\frac{\pi}{4}}^{-\frac{\pi}{2}} \cos x \, dx \right|$$ $$\Rightarrow A = \left| \frac{1}{\sqrt{2}} - 1 \right| + 1 + \frac{1}{\sqrt{2}} + \left| -1 + \frac{1}{\sqrt{2}} \right| + \left| \frac{1}{\sqrt{2}} + 1 \right|$$ $$\Rightarrow A = 2 + \frac{2}{\sqrt{2}} + 2 - \frac{2}{\sqrt{2}} = 4$$ Hence this is the required option.

Question 11

Maths · Matrices · Single correct

The number of symmetric matrices of order 3, with all the entries from the set {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} is

  1. $6^{10}$
  2. $10^{6}$
  3. $9^{10}$
  4. $10^{9}$

Answer: (b)

Solution

Given that $A = \{0, 1, 2, 3, \ldots 8, 9\}$. We need to find the number of symmetric matrices. We know that a matrix is symmetric if $A^T = A$. $$A = \begin{bmatrix} a_{11} & a_{12} & a_{13} \\ a_{21} & a_{22} & a_{23} \\ a_{31} & a_{32} & a_{33} \end{bmatrix}$$ Now $a_{11}, a_{22}, a_{33}$ can have any digit from 0 to 9. Number of ways this can be done is $10 \times 10 \times 10 = 10^3$. Now $a_{12} = a_{21}$. So number of ways this can be done is $10 \times 1$. Similarly $a_{13} = a_{31}$. So number of ways this can be done is $10 \times 1$. Also, $a_{23} = a_{32}$. So number of ways this can be done is $10 \times 1$. $\therefore$ Total symmetric matrix $= 10^3 \times 10 \times 10 \times 10 = 10^6$. Hence this is the correct option.

Question 12

Maths · Limits and Derivatives · Single correct

Among (S1): $\lim_{n \to \infty} \frac{1}{n^2} \left(2 + 4 + 6 + \ldots + 2n\right) = 1$ (S2): $\lim_{n \to \infty} \frac{1}{n^{16}} \left(1^{15} + 2^{15} + 3^{15} + \ldots + n^{15}\right) = \frac{1}{16}$

  1. Both (S1) and (S2) are true
  2. Only (S1) is true
  3. Both (S1) and (S2) are false
  4. Only (S2) is true

Answer: (a)

Solution

For $S_1$: $\lim_{n \to \infty} \frac{1}{n^2} \left[ 2 + 4 + 6 + \ldots + 2n \right]$. $$\lim_{n \to \infty} \frac{2n(n+1)}{2n^2} = 1$$ For $S_2$: $\lim_{n \to \infty} \frac{1}{n^{16}} \left( 1^{15} + 2^{15} + 3^{15} + \ldots + n^{15} \right)$. This is limit of sum. We know that $\lim_{n \to \infty} \sum_{r=1}^{n} f\left( \frac{r}{n} \right) \frac{1}{n} = \int_{0}^{1} f(x) \, dx$. Therefore, $\lim_{n \to \infty} \frac{\sum_{r=1}^{n} r^k}{n^{k+1}} = \lim_{n \to \infty} \frac{\sum_{r=1}^{n} \left( \frac{r}{n} \right)^k}{n}$. $$= \int_{0}^{1} x^k \, dx = \frac{1}{k+1}$$ Here $k = 15$. Therefore, $\lim_{n \to \infty} \frac{\sum_{r=1}^{n} r^{15}}{n^{16}} = \frac{1}{16}$. Therefore, both $S_1$ and $S_2$ are correct. Hence this is the required option.

Question 13

Maths · Conic Sections · Single correct

Let $PQ$ be a focal chord of the parabola $y^2 = 36x$ of length 100, making an acute angle with the positive $x$-axis. Let the ordinate of $P$ be positive and $M$ be the point on the line segment $PQ$ such that $PM : MQ = 3 : 1$. Then which of the following points does NOT lie on the line passing through $M$ and perpendicular to the line $PQ$?

  1. (-6, 45)
  2. (6, 29)
  3. (3, 33)
  4. (-3, 43)

Answer: (d)

Solution

We have been given the length of focal chord $PQ = 100$. Length of focal chord at $(t) = a \left( t + \frac{1}{t} \right)^2 = 100$ Where $a = 9$ $$t + \frac{1}{t} = \pm \frac{10}{3}$$ $$\therefore t = 3, \frac{1}{3}, -3, -\frac{1}{3}$$ Since ordinate of $P$ is $+\mathrm{ve}$ $$\therefore t = 3 or \frac{1}{3}$$ $(t = 3 as slope of PQ is positive)$ $$\therefore M(21, 9)$$ Required line: $y - 9 = \frac{-80}{60} \left( x - 21 \right)$ $$\Rightarrow 4x + 3y = 111$$ $(-3, 43)$ does not lie on line. Hence this is the correct option.

Question 14

Maths · Relations and Functions · Single correct

For $x \in \mathbb{R}$, two real valued functions $f(x)$ and $g(x)$ are such that, $g(x) = \sqrt{x} + 1$ and $fog(x) = x + 3 - \sqrt{x}$. Then $f(0)$ is equal to

  1. 1
  2. 5
  3. 0
  4. -3

Answer: (b)

Solution

We have been given that $$f(g(x)) = x + 3 - \sqrt{x}$$ $$\Rightarrow f(\sqrt{x} + 1) = x + 3 - \sqrt{x}$$ Put $\sqrt{x} + 1 = t$ $$\sqrt{x} = t - 1$$ $$x = (t - 1)^2$$ $$\Rightarrow f(t) = (t - 1)^2 + 3 - (t - 1)$$ $$\Rightarrow f(0) = 1 + 3 + 1 = 5$$ Hence this is the correct option.

Question 15

Maths · Binomial Theorem · Single correct

Fractional part of the number $\frac{4^{2022}}{15}$ is equal to

  1. $\frac{8}{15}$
  2. $\frac{4}{15}$
  3. $\frac{14}{15}$
  4. $\frac{1}{15}$

Answer: (d)

Solution

Given that $\frac{4^{2022}}{15}$. We know that $(a + x)^n = {}^{n}C_{0} a^n x^0 + {}^{n}C_{1} a^{n-1} x^1 + \ldots + {}^{n}C_{n} a^0 x^n$. $$\Rightarrow \frac{4^{2022}}{15} = \frac{16^{1011}}{15} = \frac{(15+1)^{1011}}{15}$$ $$= \frac{{}^{1011}C_{0} (15)^{1011} + {}^{1011}C_{1} (15)^{1010} + \ldots + {}^{1011}C_{1011} (15)^0}{15}$$ $$= {}^{1011}C_{0} (15)^{1010} + {}^{1011}C_{1} (15)^{1009} + \ldots + {}^{1011}C_{1010} (15)^1 + \frac{1}{15}$$ Therefore, the fractional part of $\frac{4^{2022}}{15} = \frac{1}{15}$. Hence this is the required option.

Question 16

Maths · Vector Algebra · Single correct

Let $\vec{a}=\hat{i}+4\hat{j}+2\hat{k}$, $\vec{b}=3\hat{i}-2\hat{j}+7\hat{k}$, and $\vec{c}=2\hat{i}-\hat{j}+4\hat{k}$. If a vector $\vec{d}$ satisfies $\vec{d}\times\vec{b}=\vec{c}\times\vec{b}$ and $\vec{d}\cdot\vec{a}=24$, then $|\vec{d}|^2$ is equal to $\underline{\hspace{2cm}}$.

  1. 323
  2. 423
  3. 313
  4. 413

Answer: (d)

Solution

We have been given that $\vec{d} \times \vec{b} = \vec{c} \times \vec{b}$. Therefore, $\left( \vec{d} - \vec{c} \right) \times \vec{b} = 0$. This implies $\vec{d} - \vec{c} = \lambda \vec{b}$ (since $\vec{d} \neq \vec{c}$). Thus, $\vec{d} = \vec{c} + \lambda \vec{b}$. It is given that $\vec{a} \cdot \vec{d} = 24$. Therefore, $\vec{a} \cdot \vec{c} + \lambda \vec{b} \cdot \vec{a} = 24$. This implies $6 + \lambda (3 - 8 + 14) = 24$. Therefore, $9 \lambda = 18$. Solving gives $\lambda = 2$. Thus, $\vec{d} = \vec{c} + 2 \vec{b}$. Therefore, $\vec{d} = 8 \hat{i} - 5 \hat{j} + 18 \hat{k}$. The magnitude of $\vec{d}$ is $|\vec{d}|^2 = 64 + 25 + 324 = 413$. Hence, this is the correct option.

Question 17

Maths · Matrices · Single correct

Let $B = \begin{bmatrix} 1 & 3 & \alpha \\ 1 & 2 & 3 \\ \alpha & \alpha & 4 \end{bmatrix}, \alpha > 2$ be the adjoint of a matrix $A$ and $|A| = 2$. Then $\begin{bmatrix} \alpha & -2\alpha & \alpha \end{bmatrix} B \begin{bmatrix} \alpha \\ -2\alpha \\ \alpha \end{bmatrix}$ is equal to

  1. 0
  2. 16
  3. -16
  4. 32

Answer: (c)

Solution

We have been given that $B = \begin{bmatrix} 1 & 3 & \alpha \\ 1 & 2 & 3 \\ \alpha & \alpha & 4 \end{bmatrix}$, $\alpha > 2$. And $adj(A) = B$, $|A| = 2$ implies $|adj(A)| = |B|$. We know that $|adjA| = |A|^{n-1}$ implies $2^2 = (8 - 3\alpha) - 3(4 - 3\alpha) + \alpha(-\alpha)$ implies $\alpha^2 - 6\alpha + 8 = 0$ implies $(\alpha - 4)(\alpha - 2) = 0$. $\alpha = 4, 2$ but $\alpha > 2$ so $\alpha = 4$. Now $\begin{bmatrix} \alpha & -2\alpha & \alpha \end{bmatrix} B = \begin{bmatrix} 4 & -8 & 4 \end{bmatrix} \begin{bmatrix} 1 & 3 & 4 \\ 1 & 2 & 3 \\ 4 & 4 & 4 \end{bmatrix} = \begin{bmatrix} 4 \\ -8 \\ 4 \end{bmatrix} = [12 12 8] = 48 - 96 + 32 = -16$. Hence this is the correct option.

Question 18

Maths · Sequences and Series · Single correct

Let $s_1, s_2, s_3, \ldots, s_{10}$ respectively be the sum of 12 terms of 10 A.Ps whose first terms are 1, 2, 3, $\ldots$, 10 and the common differences are 1, 3, 5, $\ldots$, 19 respectively. Then $\sum_{i=1}^{10} s_i$ is equal to

  1. 7220
  2. 7360
  3. 7260
  4. 7380

Answer: (c)

Solution

Given, first term of A.P are 1, 2, 3, $\ldots$ 10, so general term of the first term will be $i$. And common difference are 1, 3, 5, $\ldots$, so general term of common difference is given by $2i - 1$. Now sum of the A.P is given by, $$S_i = \frac{12}{2} [2 \times i + (12 - 1)(2i - 1)]$$ $$\Rightarrow S_i = 6 [2 \times i + 11(2i - 1)]$$ $$\Rightarrow S_i = 144i - 66$$ So, $$\sum_{i=1}^{10} S_i = \sum_{i=1}^{10} 144i - 66 \sum_{i=1}^{10} 1$$ $$\Rightarrow \sum_{i=1}^{10} S_i = 144 \left( \frac{10 \times 11}{2} \right) - 66 \times 10$$ $$\Rightarrow \sum_{i=1}^{10} S_i = 792(10) - 66 \times 10$$ $$\Rightarrow \sum_{i=1}^{10} S_i = 7260$$ Hence this is the correct option.

Question 19

Maths · Differential Equations · Single correct

Let $y = y_1(x)$ and $y = y_2(x)$ be the solution curves the differential equation $\frac{dy}{dx} = y + 7$ with initial conditions $y_1(0)= 0$ and $y_2(0)= 1$ respectively. Then the curves $y = y_1(x)$ and $y = y_2(x)$ intersect at

  1. no point
  2. two points
  3. one point
  4. infinite number of points

Answer: (a)

Solution

We have been given that $\frac{dy}{dx} = y + 7 \implies \frac{dy}{y+7} = dx$. $$\implies \ln |y + 7| = x + c$$ $$\implies |y + 7| = k \cdot e^x$$ $$\implies y = k \cdot e^x - 7$$ $$\implies y_1(0) = 0 \implies k = 7 \implies y_1(x) = 7(e^x - 1)$$ $$\implies y_2(0) = 1 \implies 1 = k - 7 \implies 8 = k$$ $$\implies y_2(x) = 8e^x - 7$$ $$\implies y_1(x) = y_2(x) \implies 8e^x - 7 = 7e^x - 7$$ Hence, No point of intersection. This is the required option.

Question 20

Maths · Three Dimensional Geometry · Single correct

Let the equation of plane passing through the line of intersection of the planes $x + 2y + az = 2$ and $x - y + z = 3$ be $5x - 11y + bz = 6a - 1$. For $c \in \mathbb{Z}$, if the distance of this plane from the point $(a, -c, c)$ is $\frac{2}{\sqrt{a}}$, then $\frac{a+b}{c}$ is equal to

  1. 2
  2. 4
  3. -4
  4. -2

Answer: (c)

Solution

Let the equation of plane passing through the intersection of two given planes: $$x + 2y + az - 2 + \lambda(x - y + z - 3) = 0$$ $$\Rightarrow x(\lambda + 1) + y(2 - \lambda) + z(a + \lambda) - 2 - 3\lambda = 0$$ This is same as $5x - 11y + bz = 6a - 1$ $$\frac{\lambda + 1}{5} = \frac{2 - \lambda}{-11} = \frac{a + \lambda}{b} = \frac{2 + 3\lambda}{6a - 1}$$ $$\Rightarrow -11\lambda - 11 = 10 - 5\lambda$$ $$\Rightarrow 6\lambda = -21 \Rightarrow \lambda = \frac{-7}{2}$$ $$\frac{2 - \lambda}{-11} = \frac{2 + 3\lambda}{6a - 1} \Rightarrow \frac{2 + \frac{7}{2}}{-11} = \frac{2 - \frac{21}{2}}{6a - 1} \Rightarrow \frac{1}{2} = \frac{-17}{2(6a - 1)} \Rightarrow 6a - 1 = 17 \Rightarrow a = 3$$ $$\frac{2 - \lambda}{-11} = \frac{a + \lambda}{b} \Rightarrow \frac{1}{2} = \frac{3 - \frac{7}{2}}{b}$$ $$\Rightarrow \frac{-b}{2} = -\frac{1}{2} \Rightarrow b = 1$$ Therefore, point $(a, -c, c) \equiv (3, -c, c)$ Distance $= \frac{2}{\sqrt{a}} = \frac{2}{\sqrt{3}}$ Plane: $5x - 11y + z = 17$ The distance of the plane from $(3, -c, c)$ is $$\left| \frac{15 + 11c + c - 17}{\sqrt{147}} \right| = \frac{2}{\sqrt{3}}$$ $$\Rightarrow |12c - 2| = 14$$ $$\Rightarrow c = -1, \frac{4}{3}$$ $$c = -1 (c \in \mathbb{Z})$$ Therefore, $\frac{a + b}{c} = \frac{3 + 1}{-1} = -4$ Hence this is the required option.

Question 21

Maths · Binomial Theorem · Numerical

Let $\alpha$ be the constant term in the binomial expansion of $\left( \sqrt{x} - \frac{6}{x^{\frac{3}{2}}} \right)^n$, $n \leq 15$. If the sum of the coefficients of the remaining terms in the expansion is 649 and the coefficient of $x^{-n}$ is $\lambda \alpha$, then $\lambda$ is equal to ________.

Answer: 36

Solution

Given, $$\left( \sqrt{x} - \frac{6}{x^{\frac{3}{2}}} \right)^n, \; n \leq 15$$ Now the $r^{th}$ term is given by $$T_{r+1} = nC_r \left( x^{\frac{1}{2}} \right)^{n-r} \left( -6x^{-\frac{3}{2}} \right)^r$$ $$\Rightarrow T_{r+1} = (-6)^r \cdot nC_r \cdot x^{\frac{n-r}{2}} \cdot x^{-\frac{3r}{2}}$$ $$\Rightarrow T_{r+1} = (-6)^r \cdot nC_r \cdot x^{\frac{n-4r}{2}}$$ Now we have to take, $n = 4r$ for constant term so $n$ is divisible by 4. So, $$\alpha = nC_{\frac{n}{4}} (-6)^{\frac{n}{4}}$$ And sum of all coefficients will be $$\left( \sqrt{1} - \frac{6}{3^{\frac{1}{2}}} \right)^n = (-5)^n$$ Also given, $$(-5)^n - nC_{\frac{n}{4}} (-6)^{\frac{n}{4}} = 649$$ Now by hit and trial we get, $n = 4$ Hence, $$\alpha = 4C_1 (-6)^{\frac{4}{4}} = -24$$ Now for coefficient of $x^{-4}$ $$\frac{n-4r}{2} = -4$$ $$\Rightarrow n = 4r - 8 \Rightarrow r = 3$$ So, $$\lambda(\alpha) = (-6)^3 \cdot 4C_3$$ $$\Rightarrow \lambda(-24) = (-6)^3 \cdot 4C_3$$ $$\Rightarrow \lambda = 36$$

Question 22

Maths · Inverse Trigonometric Functions · Numerical

If $S = \left\{ x \in \mathbb{R} : \sin^{-1} \left( \frac{x+1}{\sqrt{x^2+2x+2}} \right) - \sin^{-1} \left( \frac{x}{\sqrt{x^2+1}} \right) = \frac{\pi}{4} \right\}$ then $\sum_{x \in S} \left( \sin \left( (x^2 + x + 5) \frac{\pi}{2} \right) - \cos \left( (x^2 + x + 5) \pi \right) \right)$ is equal to _________.

Answer: 4

Solution

Given, $\sin^{-1}\left(\frac{x+1}{\sqrt{x^2+2x+2}}\right)-\sin^{-1}\left(\frac{x}{\sqrt{x^2+1}}\right)=\frac{\pi}{4}$ $\Rightarrow \sin^{-1}\left(\frac{x+1}{\sqrt{x^2+2x+2}}\right)=\frac{\pi}{4}+\sin^{-1}\left(\frac{x}{\sqrt{x^2+1}}\right)$ $\Rightarrow \sin\left(\sin^{-1}\left(\frac{x+1}{\sqrt{x^2+2x+2}}\right)\right)=\sin\left(\frac{\pi}{4}+\sin^{-1}\left(\frac{x}{\sqrt{x^2+1}}\right)\right)$ $\Rightarrow \left(\frac{x+1}{\sqrt{x^2+2x+2}}\right)=\frac{1}{\sqrt{2}}\times\frac{1}{\sqrt{x^2+1}}+\frac{1}{\sqrt{2}}\times\frac{x}{\sqrt{x^2+1}}$ $\Rightarrow \frac{x+1}{\sqrt{x^2+2x+2}}=\frac{x+1}{\sqrt{2}\sqrt{x^2+1}}$ $\Rightarrow (x+1)\left(\sqrt{2}\sqrt{x^2+1}-\sqrt{x^2+2x+2}\right)=0$ $\Rightarrow x=-1 \text{ or } \sqrt{x^2+2x+2}=\sqrt{2}\cdot\sqrt{x^2+1}$ Now solving, $\sqrt{x^2+2x+2}=\sqrt{2}\cdot\sqrt{x^2+1}$ we get, $x^2+2x+2=2(x^2+1)$ $\Rightarrow x^2-2x=0$ $\Rightarrow x=0,\;x=2$ Hence, $S=\{0,2\}$. Now solving, $\sum_{x\in S}\left(\sin\left(\frac{(x^2+x+5)\pi}{2}\right)-\cos\left((x^2+x+5)\pi\right)\right)$ $=\left(\sin\frac{5\pi}{2}-\cos5\pi\right)+\left(\sin\frac{11\pi}{2}-\cos11\pi\right)$ $=1-(-1)+1-(-1)=4$

Question 23

Maths · Complex Numbers and Quadratic Equations · Numerical

Let $w = z\overline{z} + k_1 z + k_2 i z + \lambda (1+i)$, $k_1, k_2 \in \mathbb{R}$. Let $Re(w) = 0$ be the circle $C$ of radius 1 in the first quadrant touching the line $y = 1$ and the $y$-axis. If the curve $Im(w) = 0$ intersects $C$ at $A$ and $B$, then $30(AB)^2$ is equal to .

Answer: 24

Solution

Given, $$w = \bar{z}z + k_1 z + k_2 i z + \lambda (1+i), \; k_1, k_2 \in \mathbb{R}.$$ And $\operatorname{Re}(w) = 0$, So, taking $z = x + iy$ and $\bar{z} = x - iy$ We get, $$w = x^2 + y^2 + k_1 (x + iy) + k_2 i (x + iy) + \lambda (1+i)$$ $$\Rightarrow \operatorname{Re}(w) = 0 \Rightarrow x^2 + y^2 + k_1 x - k_2 y + \lambda = 0$$ And, $\operatorname{Im}(w) = 0 \Rightarrow k_1 y + k_2 x + \lambda = 0$ Now given $\operatorname{Re}(w) = 0$ circle is touching $y = 1$ and $y$-axis, with radius 1, so we have equation of circle $$x^2 + y^2 - 2x - 4y + 4 = 0$$ So, on comparing with $\operatorname{Re}(w) = 0$ we get, $$k_1 = -2, \; k_2 = 4, \; \lambda = 4$$ So, $\operatorname{Im}(w) = 0 \Rightarrow -2y + 4x + 4 = 0$ And given $-2y + 4x + 4 = 0$ intersects the circle, So, solving $x^2 + y^2 - 2x - 4y + 4 = 0$ and $-2y + 4x + 4 = 0$ we get, Intersecting point as $A(0, 2)$ and $B\left(\frac{2}{5}, \frac{14}{5}\right)$ Hence, by distance formula we get, $$30 \left(AB\right)^2 = 30 \left( \left(0 - \frac{2}{5}\right)^2 + \left(2 - \frac{14}{5}\right)^2 \right) = 24$$

Question 24

Maths · Binomial Theorem · Numerical

Let for $x \in \mathbb{R}$, $S_0(x) = x$, $S_k(x) = C_k x + k \int_0^x S_{k-1}(t) dt$ where $C_0 = 1$, $C_k = 1 - \int_0^1 S_{k-1}(x) dx$, $k = 1, 2, 3, \ldots$ Then $S_2(3) + 6C_3$ is equal to _______.

Answer: 18

Solution

Given, $S_0(x) = x$, $S_k(x) = C_k x + k \int_0^x S_{k-1}(t) dt$. Now for $S_0(x) = x$, $C_0 = 1$. Now solving, $C_k = 1 - \int_0^1 S_{k-1}(x) dx$ for $k = 1$ we get, $$C_1 = 1 - \int_0^1 x dx = \frac{1}{2}$$ Now putting $k = 1$ in $S_k(x) = C_k x + k \int_0^x S_{k-1}(t) dt$ we get, $$\Rightarrow S_1(x) = \frac{x}{2} + 1 \cdot \int_0^x t dt = \frac{x}{2} + \frac{x^2}{2}$$ Now for $k = 2$ we get, $$C_2 = 1 - \int_0^1 \left( \frac{x}{2} + \frac{x^2}{2} \right) dx = \frac{7}{12}$$ And $$S_2(x) = \frac{7}{12} x + 2 \int_0^x \left( \frac{t}{2} + \frac{t^2}{2} \right) dt$$ $$\Rightarrow S_2(x) = \frac{7x}{12} + \frac{x^2}{2} + \frac{x^3}{3}$$ Now taking $k = 3$ we get, $$C_3 = 1 - \int_0^1 \left( \frac{7x}{12} + \frac{x^2}{2} + \frac{x^3}{3} \right) dx = \frac{11}{24}$$ Now finding the value of $S_2(3) + 6 \cdot C_3$ we get, $$S_2(3) + 6 \cdot C_3 = \frac{7 \times 3}{12} + \frac{3^2}{2} + \frac{3^3}{3} + 6 \cdot \frac{11}{24}$$ $$S_2(3) + 6 \cdot C_3 = \frac{61}{4} + \frac{11}{4} = 18$$

Question 25

Maths · Sequences and Series · Numerical

The sum to 20 terms of the series $2 \cdot 2^2 - 3^2 + 2 \cdot 4^2 - 5^2 + 2 \cdot 6^2 - \ldots$ is equal to _________.

Answer: 1310

Solution

Given, $$2 \cdot 2^2 - 3^2 + 2 \cdot 4^2 - 5^2 + 2 \cdot 6^2 - \cdots 20 terms,$$ $$= \sum_{r=1}^{10} \left( 2 \cdot (2r)^2 - (2r+1)^2 \right)$$ $$= \sum_{r=1}^{10} (8r^2 - 4r^2 - 4r - 1)$$ $$= \sum_{r=1}^{10} (4r^2 - 4r - 1)$$ $$= 4 \sum_{r=1}^{10} r^2 - 4 \sum_{r=1}^{10} r - \sum_{r=1}^{10} 1$$ $$= \frac{4 \cdot 10 \cdot 11 \cdot 21}{6} - 4 \cdot \frac{10 \cdot 11}{2} - 10$$ $$= 44 \cdot 35 - 220 - 10 = 1540 - 230 = 1310$$

Question 26

Maths · Permutations and Combinations · Numerical

The number of seven digit positive integers formed using the digits 1, 2, 3 and 4 only and sum of the digits equal to 12 is _______.

Answer: 413

Solution

The given numbers are 1, 2, 3, 4 and sum of digits should be 12. Case 1: $\underline{4 \ 3 \ 1 \ 1 \ 1 \ 1 \ 1}$. Here the sum of the digits is 12. The number of ways arranging them is $$\frac{7!}{5!} = 42.$$ Case 2: $\underline{4 \ 2 \ 2 \ 1 \ 1 \ 1 \ 1}$. The number of ways arranging them is $$\frac{7!}{2!4!} = 105.$$ Case 3: $\underline{3 \ 2 \ 2 \ 2 \ 1 \ 1 \ 1}$. The number of ways arranging them is $$\frac{7!}{3!3!} = 140.$$ Case 4: $\underline{3 \ 3 \ 2 \ 1 \ 1 \ 1 \ 1}$. The number of ways arranging them is $$\frac{7!}{2!4!} = 105.$$ Case 5: $\underline{2 \ 2 \ 2 \ 2 \ 2 \ 1 \ 1}$. The number of ways arranging them is $$\frac{7!}{5!2!} = 21.$$ The total number of ways are $$42 + 105 + 140 + 105 + 21 = 413.$$ Therefore, the required answer is 413.

Question 27

Maths · Conic Sections · Numerical

Let $m_1$ and $m_2$ be the slopes of the tangents drawn from the point $P(4, 1)$ to the hyperbola $H : \frac{y^2}{25} - \frac{x^2}{16} = 1$. If $Q$ is the point from which the tangents drawn to $H$ have slopes $|m_1|$ and $|m_2|$ and they make positive intercepts $\alpha$ and $\beta$ on the $x$-axis, then $\frac{(PQ)^2}{\alpha \beta}$ is equal to .

Answer: 8

Solution

Given that $H : \frac{y^2}{25} - \frac{x^2}{16} = 1$. Equation of tangent to the hyperbola is: $y = mx + \sqrt{25 - 16m^2}$. Passes through $(4, 1)$. $$\Rightarrow y = mx + \sqrt{25 - 16m^2}$$ $$\Rightarrow 1 = 4m + \sqrt{25 - 16m^2}$$ $$\Rightarrow 4m^2 - m - 3$$ $$\Rightarrow m_1 = 1, \ m_2 = \frac{-3}{4}$$ $$\Rightarrow |m_1| = 1, \ |m_2| = \frac{3}{4}$$ Equation of tangents with slopes $1$ and $\frac{3}{4}$ $$\Rightarrow y = x - 3 \ldots \ldots (i)$$ $$\Rightarrow y = \frac{3}{4}x - 4 \ldots \ldots (ii)$$ $(i)$ and $(ii)$ $\Rightarrow Q \equiv (-4, -7)$ $P \equiv (4, 1)$ $$\Rightarrow (PQ)^2 = 8^2 + 8^2 = 128$$ On converting $(i)$ and $(ii)$ in intercept form we get, $(i) \Rightarrow \alpha = 3, \ (ii) \Rightarrow \beta = \frac{16}{3}$ $$\Rightarrow \frac{(PQ)^2}{\alpha \beta} = \frac{128}{3 \times \frac{16}{3}} = 8$$ Hence this is the required option.

Question 28

Maths · Three Dimensional Geometry · Numerical

Let the image of the point $\left( \frac{5}{3}, \frac{5}{3}, \frac{8}{3} \right)$ in the plane $x - 2y + z - 2 = 0$ be $P$. If the distance of the point $Q(6, -2, \alpha), \alpha > 0$, from $P$ is 13, then $\alpha$ is equal to

Answer: 15

Solution

The image of the point $\left( \frac{5}{3}, \frac{5}{3}, \frac{8}{3} \right)$ with respect to the plane will be, $$\frac{x - \frac{5}{3}}{1} = \frac{y - \frac{5}{3}}{-2} = \frac{z - \frac{8}{3}}{1} = \frac{-2 \left( 1 \times \frac{5}{3} - 2 \times \frac{5}{3} + \frac{8}{3} - 2 \right)}{1^2 + 2^2 + 1^2}$$ $$\Rightarrow \frac{x - \frac{5}{3}}{1} = \frac{y - \frac{5}{3}}{-2} = \frac{z - \frac{8}{3}}{1} = \frac{-2(-1)}{6}$$ $$\Rightarrow P(x, y, z) = (2, 1, 3)$$ But $PQ = 13$ $$4^2 + 3^2 + (\alpha - 3)^2 = 169$$ $$|\alpha - 3| = 12$$ $$\alpha = 15 Since (\alpha > 0)$$ Hence this is the required answer.

Question 29

Maths · Vector Algebra · Numerical

Let $\vec{a} = 3\hat{i} + \hat{j} - \hat{k}$ and $\vec{c} = 2\hat{i} - 3\hat{j} + 3\hat{k}$. If $\vec{b}$ is a vector such that $\vec{a} = \vec{b} \times \vec{c}$ and $|\vec{b}|^2 = 50$, then $72 - \left| \vec{b} + \vec{c} \right|^2$ is equal to _________.

Answer: 66

Solution

Given, $\vec{a} = 3\hat{i} + \hat{j} - \hat{k}$ and $\vec{c} = 2\hat{i} - 3\hat{j} + 3\hat{k}$. And $\vec{b}$ is a vector such that $\vec{a} = \vec{b} \times \vec{c}$ and $|\vec{b}|^2 = 50$, Now solving, $|\vec{a}| = |\vec{b} \times \vec{c}|$ $$\Rightarrow \sqrt{3^2 + 1^2 + 1^2} = |\vec{b}| \cdot \sqrt{2^2 + 3^2 + 3^2} \cdot \sin \theta$$ $$\Rightarrow \sqrt{11} = \sqrt{50} \cdot \sqrt{22} \cdot \sin \theta$$ $$\therefore \sin \theta = \frac{1}{10} or \cos \theta = \frac{\sqrt{99}}{10}$$ Now solving, $|72 - |\vec{b} + \vec{c}|^2|$ we get, $$|72 - |\vec{b} + \vec{c}|^2|$$ $$= |72 - \left( |\vec{b}|^2 + |\vec{c}|^2 + 2|\vec{b}||\vec{c}| \cos \theta \right)|$$ $$= |72 - (50 + 22 + 2 \times 5 \sqrt{2} \cdot \sqrt{22} \frac{\sqrt{99}}{10})|$$ $$= |72 - (72 + \frac{2 \times 5 \times 2 \times 11 \times 3}{10})|$$ $$= |66| = 66$$

Question 30

Maths · Statistics · Fill in the blank

Let the mean of the data be 5. If $m$ and $\sigma^2$ are respectively the mean deviation about the mean and the variance of the data, then $\($ $\frac{3\alpha}{m + \sigma^2}$ $\)$ is equal to .

Answer: 8

Solution

Given, the mean of the below data is 5. Now finding mean we get, $$\frac{4 + 72 + 28 \times 5 + 7\alpha + 72}{64 + \alpha} = 5$$ $$\Rightarrow \alpha = 16$$ So, total number of observation will be, $\sum f_i = 80$. Now finding, mean deviation we get, $$M. D = \frac{\sum f_i |x_i - 5|}{\sum f_i}$$ $$= \frac{4 \times 4 + 24 \times 2 + 0 + 16 \times 2 + 8 \times 4}{80} = \frac{8}{5}$$ So, $m = \frac{8}{5}$. Now finding, variance we get, $$\sigma^2 = \frac{\sum f_i |x_i - 5|^2}{\sum f_i}$$ $$= \frac{4 \times 16 + 24 \times 4 + 0 + 16 \times 4 + 8 \times 16}{80}$$ $$\Rightarrow \sigma^2 = \frac{22}{5}$$ Hence, the value of $\frac{3\alpha}{m + \sigma^2} = \frac{3 \times 16}{\frac{8}{5} + \frac{22}{5}} = 8$.

Physics

Question 31

Physics · Electromagnetic Waves · Single correct

Which of the following Maxwell's equation is valid for time varying conditions but not valid for static conditions:

  1. $\oint \vec{B} \cdot \vec{dl} = \mu_0 I$
  2. $\oint \vec{E} \cdot \vec{dl} = 0$
  3. $\oint \vec{D} \cdot \vec{dA} = Q$
  4. $\oint \vec{E} \cdot \vec{dl} = - \frac{\partial \Phi_B}{\partial t}$

Answer: (d)

Solution

Maxwell's four equations describe the electric and magnetic fields arising from distributions of electric charges and currents, and how those fields change in time. The equations are as follows: $$\oint \vec{E} \cdot d\vec{A} = \frac{q}{\varepsilon_0} (1)$$ $$\oint \vec{B} \cdot d\vec{A} = 0 (2)$$ $$\oint \vec{E} \cdot d\vec{l} = -\frac{\partial \phi_B}{\partial t} (3)$$ $$\oint \vec{B} \cdot d\vec{l} = \mu_0 I (4)$$ From the above set of equations, it is clear that only the third equation is valid for time varying field. Hence, this is the correct option.

Question 32

Physics · Current Electricity · Single correct

Different combination of 3 resistors of equal resistance $R$ are shown in the figures. The increasing order for power dissipation is:

  1. $P_B < P_C < P_D < P_A$
  2. $P_C < P_D < P_A < P_B$
  3. $P_C < P_B < P_A < P_D$
  4. $P_A < P_B < P_C < P_D$

Answer: (c)

Solution

The resistances can be calculated as $$R_A = R + \frac{R}{2} = \frac{3R}{2}$$ For second circuit $$\frac{1}{R_B} = \frac{1}{2R} + \frac{1}{R} = \frac{3}{2R}$$ $$\Rightarrow R_B = \frac{2R}{3}$$ For third circuit $$R_C = \frac{R}{3}$$ For fourth circuit $$R_D = 3R$$ The formula for power is given by $P = I^2 R$. Clearly, $$P_D > P_A > P_B > P_C$$

Question 33

Physics · Ray Optics and Optical Instruments · Single correct

A vessel of depth $d$ is half filled with oil of refractive index $n_1$ and the other half is filled with water of refractive index $n_2$. The apparent depth of this vessel when viewed from above will be-

  1. $\frac{2d \left( n_1 + n_2 \right)}{n_1 + n_2}$
  2. $\frac{d \left( n_1 + n_2 \right)}{2n_1 n_2}$
  3. $\frac{d n_1 n_2}{2 \left( n_1 + n_2 \right)}$
  4. $\frac{d n_1 n_2}{\left( n_1 + n_2 \right)}$

Answer: (b)

Solution

The apparent depth formula is given by $n = \frac{Real depth}{Apparent depth}$. The apparent depth in this case is given by $$d' = \frac{d_1}{n_1} + \frac{d_2}{n_2}$$ $$\Rightarrow d' = \frac{d}{2} \left( \frac{1}{n_1} + \frac{1}{n_2} \right)$$ $$\Rightarrow d' = \frac{d}{2} \left( \frac{n_1 + n_2}{n_1 n_2} \right)$$

Question 34

Physics · Electromagnetic Induction · Single correct

The source of time varying magnetic field may be (A) a permanent magnet (B) an electric field changing linearly with time (C) direct current (D) a decelerating charge particle (E) an antenna fed with a digital signal Choose the correct answer from the options given below.

  1. and (E) only
  2. only
  3. only
  4. and (D) only

Answer: (b)

Solution

An electric field varying linearly with time will not produce variable magnetic field as current will be constant. A decelerating charged particle can result in a time varying magnetic field by emitting radiation. Similarly a permanent magnet has a constant magnetic field and a direct current does not change its direction and cannot produce a magnetic field. An antenna can modulate the digital signals. So, the right option is the statement D.

Question 35

Physics · Motion in a Straight Line · Single correct

Two trains $A$ and $B$ of length $l$ and $4l$ are travelling into a tunnel of length $L$ in parallel tracks from opposite directions with velocities $108 \, \mathrm{km} \, \mathrm{h}^{-1}$ and $72 \, \mathrm{km} \, \mathrm{h}^{-1}$, respectively. If train $A$ take $35 \, \mathrm{s}$ less time than train $B$ to cross the tunnel then, length $L$ of tunnel is: (Given $L = 60 \, l$)

  1. 1200 m
  2. 900 m
  3. 1800 m
  4. 2700 m

Answer: (c)

Solution

The time taken for $A$ $$\Delta t_A = \frac{l+L}{V_A}$$ The time taken for $B$ $$\Delta t_B = \frac{4l+L}{V_B}$$ It is given that $B$ takes more time than $A$. So, $$\Rightarrow \frac{4l+L}{20} - \frac{l+L}{30} = 35$$ $$\Rightarrow \frac{64L}{20} - \frac{61L}{30} = 35$$ $$\Rightarrow l = \frac{35 \times 600}{700} = 30 \, \mathrm{m}$$ Therefore, $$L = 1800 \, \mathrm{m}.$$

Question 36

Physics · Work, Energy and Power · Single correct

The ratio of powers of two motors is $\frac{3\sqrt{x}}{\sqrt{x+1}}$; that are capable of raising $300 \, \mathrm{kg}$ water in $5 \, \mathrm{minutes}$ and $50 \, \mathrm{kg}$ water in $2 \, \mathrm{minutes}$ respectively from a well of $100 \, \mathrm{m}$ deep. The value of $x$ will be

  1. 16
  2. 2
  3. 2.4
  4. 4

Answer: (a)

Solution

The work done in raising the water is $W = mgh$. Power is $P = \frac{W}{t}$. Let the powers of both the motors be $P_1$ and $P_2$ respectively. Hence, the ratio of the powers is, $$\frac{P_1}{P_2} = \frac{300 \times g \times 100}{5 \times 60} \div \frac{50 \times g \times 100}{2 \times 60} = \frac{60}{25}$$ $$\Rightarrow \frac{3\sqrt{x}}{\sqrt{x+1}} = 2.4$$ $$\Rightarrow 3\sqrt{x} = 2.4\sqrt{x} + 2.4$$ $$\Rightarrow x = 16$$

Question 37

Physics · Gravitation · Single correct

A planet having mass $9 \, M_e$ and radius $4 \, R_e$, where $M_e$ and $R_e$ are mass and radius of earth respectively, has escape velocity in $\mathrm{km} \, \mathrm{s}^{-1}$ given by: (Given escape velocity on earth $V_e = 11.2 \times 10^3 \, \mathrm{m} \, \mathrm{s}^{-1}$)

  1. 67.2
  2. 16.8
  3. 11.2
  4. 33.6

Answer: (b)

Solution

The escape velocity on earth is given by $V_e = \sqrt{\frac{2GM_e}{R_e}}$. Escape velocity for the planet is $$V'_{esc} = \sqrt{\frac{2G(9M_e)}{4R_e}} \cdots (i)$$ The escape velocity of earth is $V_e = 11.2 \times 10^3 \, \mathrm{m \, s^{-1}}$. From equation (i) $$V'_{esc} = \sqrt{\frac{9}{4} \left( \frac{2GM_e}{R_e} \right)} = \frac{3}{2} \times 11.2 \times 10^3 \, \mathrm{m \, s^{-1}}$$ $$\Rightarrow V'_{esc} = 16.8 \, \mathrm{km \, s^{-1}}$$

Question 38

Physics · Dual Nature of Radiation and Matter · Single correct

The difference between threshold wavelengths for two metal surfaces $A$ and $B$ having work function $\phi_A = 9 \, \mathrm{eV}$ and $\phi_B = 4.5 \, \mathrm{eV}$ in nm is: $\{$Given, $hc = 1242 \, \mathrm{eV} \, \mathrm{nm}$$\}$

  1. 540
  2. 276
  3. 264
  4. 138

Answer: (d)

Solution

The work function is given by $$\frac{hc}{\lambda} = \phi$$ which implies $$\lambda = \frac{hc}{\phi}$$ By the given data, $$\lambda_A = \frac{1242}{9} \, \mathrm{nm}, \lambda_B = \frac{1242}{4.5} \, \mathrm{nm}.$$ The difference between the wavelengths, $$\lambda_B - \lambda_A = \frac{1242}{4.5} \, \mathrm{nm} - \frac{1242}{9} \, \mathrm{nm} = \frac{1242}{9} \, \mathrm{nm} = 138 \, \mathrm{nm}$$

Question 39

Physics · Laws of Motion · Single correct

A bullet of 10 $\mathrm{g}$ leaves the barrel of gun with a velocity of 600 $\mathrm{m \, s^{-1}}$. If the barrel of gun is 50 $\mathrm{cm}$ long and mass of gun is 3 $\mathrm{kg}$, then value of impulse supplied to the gun will be:

  1. 6 $\mathrm{N \, s}$
  2. 3 $\mathrm{N \, s}$
  3. 36 $\mathrm{N \, s}$
  4. 12 $\mathrm{N \, s}$

Answer: (a)

Solution

The formula to calculate the impulse ($J$) on the gun is given by $$J = m(v - u) \ldots(1)$$ where, $m$ is the mass, $u$ is the initial velocity and $v$ is the final velocity of the bullet. Substitute the values of the known parameters into equation (1) to calculate the required impulse. $$J = 10 \, \mathrm{g} \times \frac{1 \, \mathrm{kg}}{1000 \, \mathrm{g}} \times (600 - 0) \, \mathrm{m \, s^{-1}}$$ $$= 6 \, \mathrm{N \, s}$$

Question 40

Physics · Electric Charges and Fields · Single correct

Two charges of each magnitude $0.01 \, \mathrm{C}$ and separated by a distance of $0.4 \, \mathrm{mm}$ constitute an electric dipole. If the dipole is placed in an uniform electric field $\overrightarrow{E}$ of $10 \, \mathrm{dyne} \cdot \mathrm{C}^{-1}$ making $30^\circ$ angle with $\overrightarrow{E}$, the magnitude of torque acting on dipole is:

  1. $4.0 \times 10^{-10} \, \mathrm{N} \cdot \mathrm{m}$
  2. $1.0 \times 10^{-8} \, \mathrm{N} \cdot \mathrm{m}$
  3. $1.5 \times 10^{-9} \, \mathrm{N} \cdot \mathrm{m}$
  4. $2.0 \times 10^{-10} \, \mathrm{N} \cdot \mathrm{m}$

Answer: (d)

Solution

The formula to calculate the dipole moment is given by $$|\vec{p}| = q |\vec{d}| \ldots (1)$$ Substitute the values of the known parameters into equation (1) to calculate the dipole moment. $$|\vec{p}| = 0.01 \, \mathrm{C} \times 0.4 \, \mathrm{mm} \times \frac{1 \, \mathrm{m}}{10^3 \, \mathrm{mm}}$$ $$= 4.0 \times 10^{-6} \, \mathrm{C} \cdot \mathrm{m}$$ The formula to calculate the torque on the dipole in the electric field is given by $$|\vec{\tau}| = |\vec{p} \times \vec{E}| \ldots (2)$$ Substitute the values of the known parameters into equation (2) to calculate the required torque. $$|\vec{\tau}| = 4.0 \times 10^{-6} \, \mathrm{C} \cdot \mathrm{m} \times 10 \, \mathrm{dyne} \cdot \mathrm{C}^{-1} \times \frac{1 \, \mathrm{N}}{10^5 \, \mathrm{dyne}} \times \sin 30^\circ$$ $$= 2 \times 10^{-10} \, \mathrm{N} \cdot \mathrm{m}$$

Question 41

Physics · Motion in a Plane · Single correct

A disc is rolling without slipping on a surface. The radius of the disc is $R$. At $t = 0$, the top most point on the disc is $A$ as shown in figure. When the disc completes half of its rotation, the displacement of point $A$ from its initial position is

  1. $2R$
  2. $R\sqrt{\pi^2 + 4}$
  3. $R\sqrt{\pi^2 + 1}$
  4. $2R\sqrt{1 + 4\pi^2}$

Answer: (b)

Solution

The displacement is the hypotenuse of the diameter and the distance travelled for half the rotation $\pi R$. By using Pythagoras theorem, Displacement of $A = \sqrt{(2R)^2 + (\pi R)^2}$ $$= R \sqrt{\pi^2 + 4}$$

Question 42

Physics · Physical World, Units and Measurements · Single correct

Match List-I with List-II \begin{tabular}{|c|c|c|c|} \hline & \textbf{List-I} & & \textbf{List-II} \\ & \textbf{(Layer of atmosphere)} & & \textbf{(Approximate height over earth's surface)} \\ \hline (A) & F$_1$-Layer & (I) & 10 km \\ \hline (B) & D-Layer & (II) & 170--190 km \\ \hline (C) & Troposphere & (III) & 100 km \\ \hline (D) & E-Layer & (V) & 65--75 km \\ \hline \end{tabular} Choose the correct answer from the options given below.

  1. A–II, B–IV, C–I, D–III
  2. A–II, B–IV, C–III, D–I
  3. A–III, B–IV, C–I, D–II
  4. A–II, B–I, C–IV, D–III

Answer: (a)

Solution

The $F_1$ layer is above the E layer and the ionization is less compared to E layer. It ranges to $170 - 190 \, \mathrm{km}$. The D layer is located above the stratosphere. It ranges from $60 - 90 \, \mathrm{km}$ above the earth's surface. The troposphere starts from the ground and ranges to $100 \, \mathrm{km}$. The E layer is located above the D layer. The intensity of ionization is less than the D layer. It ranges from $100 - 125 \, \mathrm{km}$ above the earth's surface.

Question 43

Physics · Kinetic Theory · Single correct

The rms speed of oxygen molecule in a vessel at particular temperature is $\left(1 + \frac{5}{x}\right)^{\frac{1}{2}} v$, when $v$ is the average speed of the molecule. The value of $x$ will be: (take $\pi = \frac{22}{7}$)

  1. 27
  2. 8
  3. 28
  4. 4

Answer: (c)

Solution

The RMS speed is given by $$v_{rms} = \sqrt{\frac{3RT}{M}}$$ The average speed is given by $$v_{avg} = \sqrt{\frac{8RT}{\pi M}}$$ The ratio is $$\Rightarrow \frac{v_{rms}}{v_{avg}} = \sqrt{\frac{\frac{3RT}{M}}{\frac{8RT}{\pi M}}} = \sqrt{\frac{3\pi}{8}} = \sqrt{\frac{3}{8} \times \frac{22}{7}}$$ $$\Rightarrow \frac{v_{rms}}{v_{avg}} = \sqrt{\frac{33}{28}}$$ Comparing it with the given value $\left(1 + \frac{5}{x}\right)^{\frac{1}{2}}$, $$\frac{v_{rms}}{v_{avg}} = \sqrt{1 + \frac{5}{28}}$$ $$\Rightarrow x = 28$$

Question 44

Physics · Work, Energy and Power · Single correct

A body of mass $(5 \pm 0.5) \, \mathrm{kg}$ is moving with a velocity of $(20 \pm 0.4) \, \mathrm{m \, s^{-1}}$. Its kinetic energy will be

  1. $(1000 \pm 0.14) \, \mathrm{J}$
  2. $(500 \pm 0.14) \, \mathrm{J}$
  3. $(500 \pm 140) \, \mathrm{J}$
  4. $(1000 \pm 140) \, \mathrm{J}$

Answer: (d)

Solution

The kinetic energy is given by, $$K = \frac{1}{2} mv^2$$ Differentiating the above equation, $$dK = \frac{1}{2} \left( v^2 dm + 2mvdv \right)$$ Dividing by $K$, $$\Rightarrow \frac{dK}{K} = \frac{dm}{m} + \frac{2dv}{v}$$ $$\Rightarrow \frac{dK}{1000} = \frac{0.5}{5} + \frac{2 \times 0.4}{20}$$ $$\Rightarrow dK = 100 + 40 = 140$$ $$\Rightarrow KE = (1000 \pm 140) \mathrm{J}$$

Question 45

Physics · System of Particles and Rotational Motion · Single correct

Two bodies are having kinetic energies in the ratio 16 : 9. If they have same linear momentum, the ratio of their masses respectively is:

  1. 3 : 4
  2. 9 : 16
  3. 16 : 9
  4. 4 : 3

Answer: (b)

Solution

The kinetic energy and the momentum of a moving object are related by $$K = \frac{p^2}{2m} \ldots (1)$$ Hence, the ratio of the kinetic energies of two objects having masses $m$ and $m'$ can be calculated as follows: $$\frac{K}{K'} = \frac{\frac{p^2}{2m}}{\frac{p^2}{2m'}}$$ $$= \frac{m'}{m} \ldots (2)$$ Substitute the ratio of the kinetic energies into equation (2) and simplify to obtain the ratio of their masses. $$\Rightarrow \frac{16}{9} = \frac{m'}{m}$$ $$\Rightarrow m : m' = 9 : 16$$

Question 46

Physics · Mechanical Properties of Fluids · Single correct

The figure shows a liquid of given density flowing steadily in horizontal tube of varying cross-section. Cross-sectional areas at $A$ is $1.5 \, \mathrm{cm}^2$, and $B$ is $25 \, \mathrm{mm}^2$, if the speed of liquid at $B$ is $60 \, \mathrm{cm} \, \mathrm{s}^{-1}$ then $(P_A - P_B)$ is (Given $P_A$ and $P_B$ are liquid pressures at $A$ and $B$ points. Density $\rho = 1000 \, \mathrm{kg} \, \mathrm{m}^{-3}$ $A$ and $B$ are on the axis of tube)

  1. $135 \, \mathrm{Pa}$
  2. $27 \, \mathrm{Pa}$
  3. $175 \, \mathrm{Pa}$
  4. $36 \, \mathrm{Pa}$

Answer: (c)

Solution

Using Bernoulli's theorem, $$P_A + \frac{1}{2} \rho V_A^2 = P_B + \frac{1}{2} \rho V_B^2 \cdots (i)$$ Using equation of continuity, $$A_A V_A = A_B V_B$$ So, $1.5 \times 10^{-4} \times V_A = 25 \times 10^{-6} \times V_B$ $$V_A = \frac{25 \times 10^{-6}}{1.5 \times 10^{-4}} \times 0.6$$ $$= \frac{1}{10} \, \mathrm{m \, s^{-1}}$$ Substituting in equation (i) $$\Rightarrow P_A - P_B = \frac{1000}{2} \left[ 0.6^2 - 0.1^2 \right] = \frac{1000}{2} \times 0.7 \times 0.5$$ $$= 175 \, \mathrm{Pa}$$

Question 47

Physics · Mechanical Properties of Solids · Single correct

Under isothermal condition, the pressure of a gas is given by $P = aV^{-3}$, where $a$ is a constant and $V$ is the volume of the gas. The bulk modulus at constant temperature is equal to

  1. $3P$
  2. $P$
  3. $2P$
  4. $\frac{P}{2}$

Answer: (a)

Solution

The data given is $$P = aV^{-3}$$ Bulk modulus is given by, $$B = -\frac{dP}{dV} \cdot \frac{V}{P} = -V \frac{dP}{dV}$$ $$= -V \frac{d}{dV} \left\{ \frac{a}{V^3} \right\}$$ $$= -V \left[ \frac{-3a}{V^4} \right]$$ $$= \frac{3a}{V^3} = 3P$$

Question 48

Physics · Semiconductor Electronics: Materials, Devices and Simple Circuits · Single correct

For the following circuit and given inputs $A$ and $B$, choose the correct option for output $Y$.

Answer: (a)

Solution

The signal $A$ is given to a NOR gate and $B$ is given to an OR gate. The output of these two signals is given to a NAND gate. Using the laws of Boolean algebra, $$Y = \overline{\overline{A} \cdot B} = A + \overline{B}.$$ Analyzing from the input graphs, one can see, $$t_1 - t_2: A = 0, \overline{B} = 0, Y = 0$$ $$t_2 - t_3: A = 1, \overline{B} = 0, Y = 1$$ $$t_3 - t_4: A = 0, \overline{B} = 1, Y = 1$$ $$t_4 - t_5: A = 1, \overline{B} = 0, Y = 1$$ $$t_5 - t_6: A = 1, \overline{B} = 1, Y = 1$$

Question 49

Physics · Oscillations · Single correct

Which graph represents the difference between total energy and potential energy of a particle executing SHM vs its distance from mean position?

Answer: (b)

Solution

In a SHM, mechanical energy is conserved. So, the sum of kinetic energy and potential energy remains constant. For a SHM, $$T.E. - U = K.E$$ $$\Rightarrow T.E. - U = \frac{1}{2} mv^2 = \frac{1}{2} m \omega^2 \left( A^2 - x^2 \right)$$ This is the equation of a downward parabola.

Question 50

Physics · Nuclei · Single correct

\[ {}^{238}_{92}A \;\rightarrow\; {}^{234}_{90}B + {}^{4}_{2}D + Q \] In the given nuclear reaction, the approximate amount of energy released will be: [Given, mass of ${}^{238}_{92}$\mathrm{A}$ = 238.05079 $\times$ 931.5 $\mathrm{MeV/c^{-2}}$, mass of ${}^{234}_{90}\mathrm{B}$ = 234.04363 $\times$ 931.5 $\mathrm{MeV/c^{-2}}$, mass of ${}^{4}_{2}\mathrm{D}$ = 4.00260 $\times$ 931.5 $\mathrm{MeV/c^{-2}}$]

  1. 3.82 $\mathrm{MeV}$
  2. 5.9 $\mathrm{MeV}$
  3. 2.12 $\mathrm{MeV}$
  4. 4.25 $\mathrm{MeV}$

Answer: (d)

Solution

The value of $Q$ is $$Q = (m_A - m_B - m_D) \times 931.5 \, \mathrm{MeV}$$ $$\Rightarrow Q = (238.05079 - 234.04363 - 4.00260) \times 931.5 \, \mathrm{MeV}$$ $$\Rightarrow Q = 4.25 \, \mathrm{MeV}$$

Question 51

Physics · Mechanical Properties of Solids · Numerical

The elastic potential energy stored in a steel wire of length 20 m stretched through 2 cm is 80 J. The cross sectional area of the wire is _____ mm$^2$. (Given, $Y = 2.0 \times 10^{11} \, \mathrm{N} \, \mathrm{m}^{-2}$)

Answer: 40

Solution

The formula to calculate the Young's modulus of the material is given by $$Y = \frac{stress}{strain} = \frac{stress}{\frac{\Delta l}{L}} \cdots (1)$$ The formula to calculate the potential energy $(U)$ stored into the wire is given by $$U = \frac{1}{2} \times stress \times strain \times volume$$ $$= \frac{1}{2} \times stress \times \frac{\Delta l}{L} \times A \times L$$ $$= \frac{1}{2} \times stress \times A \times \Delta l \cdots (2)$$ From equation (1) and equation (2), it can be written that $$U = \frac{1}{2} \times Y \times \left(\frac{\Delta l}{L}\right)^2 \times A \cdots (3)$$ Substitute the values of the known parameters into equation (3) and solve to calculate the required cross-sectional area of the wire. $$80 \, J = \frac{1}{2} \times 2.0 \times 10^{11} \, Nm^{-2} \times \left(\frac{0.02 \, m}{20 \, m}\right)^2 \times A$$ $$\Rightarrow A = \frac{2 \times 80 \, J \times 20}{2.0 \times 10^{11} \times 4 \times 10^{-4} \, Nm^{-1}}$$ $$= 4 \times 10^{-5} \, m^2 \times \frac{10^6}{1 \, m^2}$$ $$= 40 \, mm^2$$

Question 52

Physics · Current Electricity · Numerical

A potential $V_0$ is applied across a uniform wire of resistance $R$. The power dissipation is $P_1$. The wire is then cut into two equal halves and a potential of $V_0$ is applied across the length of each half. The total power dissipation across two wires is $P_2$. The ratio of $P_2 : P_1$ is $\sqrt{x} : 1$. The value of $x$ is _____.

Answer: 16

Solution

The formula to calculate the power dissipated in the first case can be written as $$P_1 = \frac{V_0^2}{R} \ldots (1)$$ When the wire is halved, its resistance will also become half the previous value. Thus, the formula to calculate the power dissipated in the second case can be written as $$P_2 = \frac{V_0^2}{\frac{R}{2}} \times 2$$ $$= \frac{4V_0^2}{R} \ldots (2)$$ Divide equation (2) by equation (1) to calculate the required ratio. $$\frac{P_2}{P_1} = \frac{\frac{4V_0^2}{R}}{\frac{V_0^2}{R}}$$ $$= 4$$ $$= \sqrt{16}$$ Hence, $\($ z = 16 $\)$.

Question 53

Physics · Oscillations · Numerical

At a given point of time the value of displacement of a simple harmonic oscillator is given as $y = A \cos(3\theta)$. If amplitude is $40 \, \mathrm{cm}$ and kinetic energy at that time is $200 \, \mathrm{J}$, the value of force constant $1.0 \times 10^x \, \mathrm{N} \, \mathrm{m}^{-1}$. The value of $x$ is _____.

Answer: 4

Solution

The formula to calculate the kinetic energy $(K)$ of a particle executing SHM is given by $$K = \frac{1}{2} k (A^2 - y^2) \ldots (1)$$ Substitute the values of the known parameters into equation (1) and solve to calculate the value of the unknown parameter. $$K = \frac{1}{2} \times k \times (A^2 - A^2 \cos^2 30^\circ)$$ $$= \frac{1}{2} \times k \times A^2 \sin^2 30^\circ$$ $$\Rightarrow 200 = \frac{1}{2} \times 1.0 \times 10^x \times (0.4)^2 \times \left(\frac{1}{2}\right)^2$$ $$= \frac{2 \times 10^x}{100}$$ $$\Rightarrow 10^2 = 10^{x-2}$$ $$\Rightarrow x - 2 = 2$$ $$\Rightarrow x = 4$$

Question 54

Physics · Current Electricity · Numerical

When a resistance of 5 $\Omega$ is shunted with a moving coil galvanometer, it shows a full scale deflection for a current of 250 mA, however when 1050 $\Omega$ resistance is connected with it in series, it gives full scale deflection for 25 volt. The resistance of galvanometer is $\Omega$.

Answer: 50

Solution

The formula to calculate the maximum current through the galvanometer, when a shunt resistance $r_1$ is connected is given by $$(i_G)_{\max} = \frac{r_1}{r_1 + R_G} i_{\max} \ldots (1)$$ When a series resistance $r_2$ is connected, the potential difference across the galvanometer is given by $$V = (i_G)_{\max} [R_G + r_2] \ldots (2)$$ From equations (1) and (2), it can be written that $$V = \frac{r_1}{r_1 + R_G} i_{\max} (R_G + r_2)$$ $$\Rightarrow V r_1 + V R_G = i_{\max} r_1 R_G + i_{\max} r_1 r_2$$ $$\Rightarrow (V - i_{\max} r_1) R_G = i_{\max} r_1 r_2 - V r_1$$ $$\Rightarrow R_G = \frac{i_{\max} r_1 r_2 - V r_1}{V - i_{\max} r_1} \ldots (3)$$ Substitute the values of the known parameters into equation (3) to calculate the required galvanometer resistance. $$R_G = \frac{0.250 \, \mathrm{A} \times 5 \, \Omega \times 1050 \, \Omega - 25 \, \mathrm{V} \times 5 \, \Omega}{25 \, \mathrm{V} - 0.250 \, \mathrm{A} \times 5 \, \Omega}$$ $$= 50 \, \Omega$$

Question 55

Physics · Atoms · Numerical

The radius of $2^{nd}$ orbit of $He^+$ of Bohr's model is $r_1$ and that of fourth orbit of $Be^{3+}$ is represented as $r_2$. Now the ratio $\frac{r_2}{r_1}$ is $x : 1$. The value of $x$ is _____.

Answer: 2

Solution

The formula to calculate the radius (r) of any nth Bohr's orbit is given by $$r = r_0 \frac{n^2}{Z} \ldots (1)$$ where, $r_0$ is Bohr's radius, $n$ is the principal quantum number and $Z$ is the atomic number. Thus, for Helium ion, $$r_1 = r_0 \frac{2^2}{2}$$ $$= 2r_0 \ldots (2)$$ And, for the Beryllium ion, $$r_2 = r_0 \frac{4^2}{4}$$ $$= 4r_0 \ldots (3)$$ Divide equation (3) by equation (2) to obtain the required ratio. $$\frac{r_2}{r_1} = \frac{4r_0}{2r_0}$$ $$= 2$$ Hence, $x = 2$.

Question 56

Physics · Electric Charges and Fields · Numerical

A thin infinite sheet charge and an infinite line charge of respective charge densities +$\sigma$ and +$\lambda$ are placed parallel at 5 $\,$ $\mathrm{m}$ distance from each other. Points P and Q are at $\frac{3}{\pi}$ $\,$ $\mathrm{m}$ and $\frac{4}{\pi}$ $\,$ $\mathrm{m}$ perpendicular distances from line charge towards sheet charge, respectively. E_p and E_q are the magnitudes of resultant electric field intensities at point P and Q respectively. If $\frac{E_p}{E_q}$ = $\frac{4}{a}$ for 2|$\sigma$| = |$\lambda$|, then the value of a is .

Answer: 6

Solution

Let's consider the following diagram: The formula to calculate the electric field due to an infinitely long charged sheet is given by $$E_s = \frac{\sigma}{2\varepsilon_0} \ldots (1)$$ The formula to calculate the electric field due to an infinitely long line charge is given by $$E_l = \frac{\lambda}{2\pi\varepsilon_0 r} \ldots (2)$$ Using equations (1) and (2), the electric field at $P$ can be calculated as follows: $$E_P = \left| \frac{\sigma}{2\varepsilon_0} - \frac{1}{4\pi\varepsilon_0} \frac{2\lambda}{3\pi} \right|$$ $$= \left| \frac{\sigma}{2\varepsilon_0} - \frac{\lambda}{6\varepsilon_0} \right|$$ $$= \frac{\sigma}{6\varepsilon_0} \ldots (3)$$ Similarly, the electric field at $Q$ is given by $$E_Q = \left| \frac{\sigma}{2\varepsilon_0} - \frac{1}{4\pi\varepsilon_0} \frac{2\lambda}{4\pi} \right|$$ $$= \left| \frac{\sigma}{2\varepsilon_0} - \frac{\lambda}{8\varepsilon_0} \right|$$ $$= \frac{\sigma}{4\varepsilon_0} \ldots (4)$$ Divide equation (3) by equation (4) to obtain the required ratio. $$\frac{E_P}{E_Q} = \frac{\frac{\sigma}{6\varepsilon_0}}{\frac{\sigma}{4\varepsilon_0}}$$ $$= \frac{4}{6}$$ Hence, $a = 6$.

Question 57

Physics · Electromagnetic Induction · Numerical

In the given figure, an inductor and resistor are connected in series with a battery of emf $E$ volt. $\frac{E^a}{2b} \, \mathrm{J} \, \mathrm{s}^{-1}$ represents the maximum rate at which the energy is stored in the magnetic field (inductor). The numerical value of $\frac{b}{a}$ will be _____.

Answer: 25

Solution

The formula to calculate the current flowing through an L-R circuit is given by $$i = \frac{E}{R} \left[ 1 - e^{-\frac{Rt}{L}} \right] \ldots (1)$$ The energy stored within the inductor can be calculated as follows: $$E_{induction} = \frac{1}{2} L i^2$$ $$= \frac{1}{2} L \frac{E^2}{R^2} \left[ 1 - e^{-\frac{Rt}{L}} \right]^2 \ldots (2)$$ The rate of change of energy stored within the inductor is given by $$\frac{d}{dt} (E_{induction}) = 2 \left[ 1 - e^{-\frac{Rt}{L}} \right] \cdot e^{-\frac{Rt}{L}} \cdot \frac{R}{L} \cdot \frac{E^2 L}{2R^2}$$ $$= \frac{E^2}{R} \left[ e^{-\frac{Rt}{L}} - e^{-\frac{2Rt}{L}} \right] \ldots (3)$$ For maximum rate, $$\frac{d^2 E}{dt^2} = 0 \ldots (4)$$ From equation (3) and (4), it can be written that $$\frac{d}{dt} \left[ \frac{E^2}{R} \left[ e^{-\frac{Rt}{L}} - e^{-\frac{2Rt}{L}} \right] \right] = 0$$ $$\Rightarrow e^{-\frac{Rt}{L}} = 2 e^{-\frac{2Rt}{L}}$$ $$\Rightarrow e^{\frac{Rt}{L}} = 2 \ldots (5)$$ From equation (3) and (5), it can be written, under maximum energy stored condition for the circuit, that $$\frac{d}{dt} (E_{induction}) = \frac{E^2}{R} \left[ 2^{-1} - 2^{-2} \right]$$ $$= \frac{E^2}{4R}$$ Substitute the values of the resistance and compare with the given expression to obtain the values of the parameters. $$a = 2$$ $$b = 2R$$ $$= 50$$ Hence, the required ratio is given by $$\frac{b}{a} = 25$$

Question 58

Physics · Ray Optics and Optical Instruments · Numerical

A fish rising vertically upward with a uniform velocity of $8 \, \mathrm{m \, s^{-1}}$, observes that a bird is diving vertically downward towards the fish with the velocity of $12 \, \mathrm{m \, s^{-1}}$. If the refractive index of water is $\frac{4}{3}$, then the actual velocity of the diving bird to pick the fish, will be__________ $\mathrm{m \, s^{-1}}$.

Answer: 3

Solution

Let the fish be at a depth $x$ from the surface and let the bird be at height $y$ from the surface. So, with respect to fish $$y' = \, \mu y + x$$ $$\Rightarrow \, y' = \frac{4y}{3} + x$$ Differentiating with respect to time, $$\frac{dy'}{dt} = \frac{4dy}{3dt} + \frac{dx}{dt}$$ $$\Rightarrow \frac{4y}{3} + \frac{dx}{dt} = -12$$ $$\Rightarrow \frac{4}{3} \cdot \frac{dy}{dt} = -12 + 8 = -4$$ $$\Rightarrow \frac{dy}{dt} = -3 \, \mathrm{m \, s^{-1}}$$

Question 59

Physics · System of Particles and Rotational Motion · Numerical

A solid sphere is rolling on a horizontal plane without slipping. If the ratio of angular momentum about axis of rotation of the sphere to the total energy of moving sphere is $\pi : 22$ then, the value of its angular speed will be________rad s$^{-1}$.

Answer: 4

Solution

The angular momentum is given by $$L = I_{CM} \omega = \frac{2MR^2 \omega}{5}$$ The total kinetic energy is $$E = \frac{1}{2} \left( Mv^2 + \frac{2MR^2 \omega^2}{5} \right)$$ The ratio of angular momentum and kinetic energy is $$\frac{L}{E} = \frac{I_{CM} \omega}{\frac{1}{2} Mv^2 + \frac{2}{5} MR^2 \omega^2} = \frac{\frac{2}{5} MR^2 \omega}{\frac{7}{10} MR^2 \omega^2}$$ $$\Rightarrow \frac{\pi}{22} = \frac{4}{7} \cdot \frac{1}{\omega} \Rightarrow \omega = 4 \, \mathrm{rad} \, \mathrm{s}^{-1}$$

Question 60

Physics · Semiconductor Electronics: Materials, Devices and Simple Circuits · Numerical

From the given transfer characteristic of a transistor in CE configuration, the value of power gain of this configuration is $10^x$, for $R_B = 10 \, \mathrm{k}\Omega$, and $R_C = 1 \, \mathrm{k}\Omega$. The value of $x$ is _____.

Answer: 3

Solution

The formula to calculate the current gain ($\beta$) in CE configuration is given by $$\beta = \frac{\Delta I_C}{\Delta I_B} \ldots(1)$$ Considering the third and the first points on the given graph, the current gain can be calculated as follows: $$\beta = \frac{(30 - 10) \times 10^{-3} \, \mathrm{A}}{(300 - 100) \times 10^{-6} \, \mathrm{A}}$$ $$= 100$$ The formula to calculate the power gain ($P$) in CE mode can be written as $$P = \beta^2 \cdot \frac{R_C}{R_B} \ldots(2)$$ Substitute the known values of the parameters into equation (2) and solve to calculate the required unknown parameter. $$10^x = 100^2 \times \frac{1 \, \mathrm{k}\Omega}{10 \, \mathrm{k}\Omega}$$ $$= 1000$$ $$= 10^3$$ $$\Rightarrow x = 3$$

Chemistry

Question 61

Chemistry · Amines · Single correct

In the reaction given below

  1. MeHN COOH
  2. MeHN CHO

Answer: (a)

Solution

The mechanism of basic amide hydrolysis begins with the nucleophilic addition of a hydroxide ion at the carbonyl carbon creating a tetrahedral alkoxide intermediate. In the given case ring opening reaction takes place. On acidification, we get a secondary amino acid.

Question 62

Chemistry · Hydrogen · Single correct

Given below are two statements: Statement I: Permutit process is more efficient compared to the synthetic resin method for the softening of water. Statement II: Synthetic resin method results in the formation of soluble sodium salts. In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Both the statements I and II are incorrect
  2. Statement I is incorrect but statement II is correct
  3. Both the statements I and II are correct
  4. Statement I is correct but statement II is incorrect

Answer: (a)

Solution

The difference between the zeolite and ion exchange process is that the zeolite process uses the mineral zeolite as the exchanging resin for cations in the hard water whereas the ion exchange process includes several different resins for the ion exchange. Synthetic resins method is more efficient as it can exchange both cations and anions.

Question 63

Chemistry · Co-ordination Compounds · Single correct

The mismatched combinations are A. Chlorophyll–Co B. Water hardness–EDTA C. Photography–$[\mathrm{Ag(CN)_2}]^-$ D. Wilkinson catalyst–$[(\mathrm{Ph_3 P})_3 \mathrm{RhCl}]$ E. Chelating ligand–D–Penicillamine Choose the correct answer from the options given below.

  1. A, C and E only
  2. A and C only
  3. A and E only
  4. D and E only

Answer: (b)

Solution

The chlorophyll molecule has a central magnesium atom engulfed by a nitrogen-containing structure called a porphyrin ring; attached to the ring is a long carbon-hydrogen side chain. Hardness of water is determined by titrating with a standard solution of ethylene diamine tetra acetic acid (EDTA) which is a complexing agent. Since EDTA is insoluble in water, the disodium salt of EDTA is taken for this experiment. EDTA can form four or six coordination bonds with a metal ion. Silver bromide is used in photography as a component of an emulsion that helps develop a photographic image. Silver bromide is sensitive to light, and when suspended in gelatin, silver bromide's grains create a photographic emulsion. Wilkinson's catalyst is the common name for chloridotris(triphenylphosphine)rhodium(I), a coordination complex of rhodium with the formula $[(\mathrm{Ph}_3 \mathrm{P})_3 \mathrm{RhCl}]$. D-Penicillamine is chelating ligand.

Question 64

Chemistry · Chemical Bonding and Molecular Structure · Single correct

In which of the following processes, the bond order increases and paramagnetic character changes to diamagnetic one?

  1. $\mathrm{O_2 \rightarrow O_2^+}$
  2. $\mathrm{O_2 \rightarrow O_2^{2-}}$
  3. $\mathrm{NO \rightarrow NO^+}$
  4. $\mathrm{N_2 \rightarrow N_2^+}$

Answer: (c)

Solution

The table shows the process, change in magnetic nature, and bond order change for different molecules. For the process $\mathrm{N_2 \rightarrow N_2^+}$, the change is from diamagnetic to paramagnetic with a bond order change from 3 to 2.5. For $\mathrm{NO \rightarrow NO^+}$, the change is from paramagnetic to diamagnetic with a bond order change from 2.5 to 3. For $\mathrm{O_2 \rightarrow O_2^{2-}}$, the change is from paramagnetic to diamagnetic with a bond order change from 2 to 1. For $\mathrm{O_2 \rightarrow O_2^+}$, the change is from paramagnetic to paramagnetic with a bond order change from 2 to 2.5.

Question 65

Chemistry · The p-Block Elements (Group 15, 16, 17 & 18) · Single correct

The incorrect statement from the following for borazine is:

  1. It contains banana bonds
  2. It can react with water
  3. It is a cyclic compound
  4. It has electronic delocalization

Answer: (a)

Solution

The statement "It contains a banana bond" is incorrect about Borazine. Borazine, also known as inorganic benzene or borazole, is a chemical compound with the formula $\mathrm{B_3N_3H_6}$. Borazine is a hexagonal planar molecule with alternating boron and nitrogen atoms, and it exhibits some structural and chemical similarities to benzene. Borazine is an aromatic compound with electron delocalization. It does not contain banana bond. On heating, borazine hydrolyses slowly. $\mathrm{B_3N_3H_6 + 9H_2O \rightarrow 3NH_3 + 3H_3BO_3 + 3H_2O}$

Question 66

Chemistry · Chemical Bonding and Molecular Structure · Single correct

Among the following compounds, the one which shows highest dipole moment is

Answer: (d)

Solution

The compound which possess aromatic character will show highest dipole moment. From the given compounds the following compound will have the highest dipole moment. Because the positive and negative ends acquire aromaticity.

Question 67

Chemistry · Amines · Single correct

Match the following \begin{tabular}{|c|c|c|l|} \hline & \textbf{Column--A} & & \textbf{Column--B} \\ \hline a. & Nylon 6 & I. & Natural Rubber \\ \hline b. & Vulcanized Rubber & II. & Cross Linked \\ \hline c. & cis-1,4-polyisoprene & III. & Caprolactam \\ \hline d. & Polychloroprene & IV. & Neoprene \\ \hline \end{tabular} Choose the correct answer from options given below:

  1. a $\to$ III, b $\to$ II, c $\to$ I, d $\to$ IV
  2. a $\to$ III, b $\to$ IV, c $\to$ I, d $\to$ II
  3. a $\to$ IV, b $\to$ III, c $\to$ II, d $\to$ I
  4. a $\to$ II, b $\to$ III, c $\to$ IV, d $\to$ I

Answer: (a)

Solution

Nylon 6 or polycaprolactam is a polymer, in particular semicrystalline polyamide. Vulcanization is a chemical process in which the rubber is heated with sulphur, accelerator and activator at $140$–$160 \, ^\circ \mathrm{C}$. The process involves the formation of cross-links between long rubber molecules to achieve improved elasticity, resilience, tensile strength, viscosity, hardness and weather resistance. Polychloroprene is the polymer name for the synthetic rubber known as neoprene. Natural rubber is the only addition polymer found in nature and is known as Cis - 1,4 - polyisoprene.

Question 68

Chemistry · Alcohols, Phenols and Ethers · Single correct

In the above reaction, left hand side and right hand side rings are named as ‘A’ and ‘B’ respectively. They undergo ring expansion. The correct statement for this process is:

  1. Ring expansion can go upto seven membered rings
  2. Finally both rings will become six membered each.
  3. Finally both rings will become five membered each.
  4. Only A will become 6 membered.

Answer: (b)

Solution

The reaction proceeds through a carbocation intermediate. The carbocation formed undergoes rearrangement by ring expansion. Four-membered ring undergoes ring expansion to a five-membered ring and the five-membered ring undergoes ring expansion to a six-membered ring and finally it converts to alkene by losing a proton.

Question 69

Chemistry · Environmental Chemistry · Single correct

The radical which mainly causes ozone depletion in the presence of UV radiations is:

  1. $\mathrm{Cl} \cdot$
  2. $\mathrm{NO} \cdot$
  3. $\mathrm{OH} \cdot$
  4. $\mathrm{CH}_3 \cdot$

Answer: (a)

Solution

Chlorofluorocarbons are chemicals which contain carbon, chlorine and fluorine. Ozone layer breaks when these CFC's are released into the atmosphere. So, chlorine is one of the radicals which belongs to CFC's family, responsible for breakdown.

Question 70

Chemistry · Haloalkanes and Haloarenes · Single correct

In the following reaction $X$ is

  1. CH_3 (CH_2)_4 CH_2 Cl
  2. Cl-CH_2-(CH_2)_4-CH_2-Cl

Answer: (a)

Solution

When n-Hexane is heated with anhydrous $AlCl_3$ and $HCl$ gas at $573\ K$ under a pressure of about $30-35\ atm$ it Isomerises to give a branched chain alkanes. $CH_3(CH_2)_4CH_3\xrightarrow[\Delta]{\text{Anhy.}\ AlCl_3,\ HCl}(CH_3)_2CHCH_2CH_2CH_3+3\text{-methylpentane}$ $2\text{-methylpentane}$ Major product in the above reaction is $2\text{-methylpentane}$.

Question 71

Chemistry · Haloalkanes and Haloarenes · Single correct

2--Methyl propyl bromide reacts with $C_2H_5O$-- and gives ‘A’ whereas on reaction with $C_2H_5 OH$ it gives ‘B’. The mechanism followed in these reactions and the products ‘A’ and ‘B’ respectively are:

  1. $S_N2$, A $=$ iso-butyl ethyl ether; $S_N1$, B $=$ tert-butyl ethyl ether
  2. $S_N1$, A $=$ tert-butyl ethyl ether; $S_N1$, B $=$ 2-butyl ethyl ether
  3. $S_N2$, A $=$ 2-butyl ethyl ether; $S_N2$, B $=$ iso-butyl ethyl ether
  4. $S_N1$, A $=$ tert-butyl ethyl ether; $S_N2$, B $=$ iso-butyl ethyl ether

Answer: (a)

Solution

The reaction between methyl propyl bromide and $\mathrm{C_2H_5O^-}$ proceeds via an $\mathrm{S_N2}$ (substitution nucleophilic bimolecular) mechanism. In this mechanism, the nucleophile attacks the carbon atom bearing the bromine (the electrophilic carbon) in a single step, leading to the displacement of the bromine atom. $$(i) Br \xrightarrow{\mathrm{C_2H_5O^-}} \mathrm{OC_2H_5}$$ $\mathrm{C_2H_5O^-}$ is a strong nucleophile. The reaction between methyl propyl bromide and $\mathrm{C_2H_5OH}$ can proceed via either an $\mathrm{S_N1}$ (substitution nucleophilic unimolecular). Here $\mathrm{C_2H_5OH}$ is a weak nucleophile. During the reaction 1,2-hydrogen shift will occur and tert-butyl ethyl ether is formed. $$(ii) Br \xrightarrow{\mathrm{C_2H_5OH}} \mathrm{CH_2^+} \xrightarrow{1,2 - H shift} (+)$$ $$\mathrm{C_2H_5OH} \xrightarrow{-\mathrm{H^+}} \mathrm{OC_2H_5}$$ $\mathrm{C_2H_5OH}$ is a weak nucleophile.

Question 72

Chemistry · Organic Chemistry — Some Basic Principles & Techniques · Single correct

The products formed in the above reaction are

  1. One optically active and one meso product
  2. Two optically inactive products
  3. Two optically active products
  4. One optically inactive and one meso product

Answer: (a)

Solution

The aldehyde group of glyceraldehyde reacts with hydrogen cyanide to give cyanohydrin. Two isomers are formed in the above step because the aldehyde is planar and changed to a tetrahedral center. On hydrolysis, the cyanide group converts to a carboxylic acid. Upon reaction with nitric acid, the primary alcoholic group undergoes oxidation to a carboxylic acid group. One compound is a meso compound, optically inactive, and the other compound is optically active.

Question 73

Chemistry · General Principles and Processes of Isolation of Elements · Single correct

Which one of the following is most likely a mismatch?

  1. Zinc-Liquation
  2. Copper-Electrolysis
  3. Nickel-Mond process
  4. Titanium-van Arkel Method

Answer: (a)

Solution

Mond's process involves the combination of carbon monoxide with nickel readily and reversibly and gives nickel tetracarbonyl. This process is used to extract and purify nickel. The Van Arkel technique is used to refine Zirconium or Titanium. Impurities found in Zirconium or Titanium in the form of nitrogen and oxygen are eliminated using this technique. Copper is purified by electrolysis. Electricity is passed through solutions containing copper compounds, such as copper sulphate. The anode (positive electrode) is made from impure copper and the cathode (negative electrode) is made from pure copper. Mercury and zinc are purified by distillation method. Liquation is a metallurgical method to remove lead containing silver from copper and remove antimony minerals from ore.

Question 74

Chemistry · Chemical Bonding and Molecular Structure · Single correct

$\mathrm{ClF}_5$ at room temperature is a

  1. Colourless liquid with trigonal bipyramidal geometry
  2. Colourless gas with square pyramidal geometry
  3. Colourless gas with trigonal bipyramidal geometry
  4. Colourless liquid with square pyramidal geometry

Answer: (d)

Solution

Chlorine pentafluoride is an inter halogen compound. $\mathrm{ClF_5}$ is a colourless liquid. The central chlorine atom is having five bond pairs and one lone pair on it. Hence, according to VSEPR theory it has square pyramidal geometry. It is toxic by inhalation and an irritant to skin, eyes and mucus membranes.

Question 75

Chemistry · The s-Block Elements · Single correct

$\mathrm{Be(OH)_2}$ reacts with $\mathrm{Sr(OH)_2}$ to yield an ionic salt. Choose the incorrect option related to this reaction from the following.

  1. Both Sr and Be elements are present in the ionic salt
  2. Be is tetrahedrally coordinated in the ionic salt
  3. The element Be is present in the cationic part of the ionic salt
  4. The reaction is an example of acid-base neutralization reaction

Answer: (c)

Solution

$\mathrm{Be(OH)_2}$ has amphoteric nature. $\mathrm{Sr(OH)_2}$ has basic nature. These two compounds undergo acid-base reaction to get salt, $$\mathrm{Be(OH)_2 + Sr(OH)_2 \rightarrow Sr^{+2}}[Be(OH)_4]^{-2}$$ As Be is present in anionic part.

Question 76

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

In the reaction given below 'B' is:

Answer: (d)

Solution

In the first step, protonation of alcohol takes place which leads to the formation of carbocation. Ring expansion takes place in the next step. In the given process, the five-membered ring becomes a six-membered ring. Now, the carbocation loses a proton in the presence of potassium hydroxide to give alkene.

Question 77

Chemistry · Classification of Elements and Periodicity in Properties · Single correct

Which of the following statements are not correct? A. The electron gain enthalpy of F is more negative than that of Cl. B. Ionization enthalpy decreases in a group of periodic table. C. The electronegativity of an atom depends upon the atoms bonded to it. D. Al$_2$O$_3$ and NO are examples of amphoteric oxides. Choose the most appropriate answer from the options given below:

  1. A, B, C and D
  2. A, B and D only
  3. B and D only
  4. A, C and D only

Answer: (d)

Solution

A is incorrect. F and Cl belong to the same group of the periodic table. The electron gain enthalpy usually becomes less negative on moving down a group. However, in this case, the value of the electron gain enthalpy of Cl is more negative than that of F. This is because the atomic size of F is smaller than that of Cl. B is correct (ionisation energy decreases down the group). C is incorrect (Electronegativity is a fixed property of an element and is typically measured on scales such as the Pauling scale or the Mulliken scale.). D is incorrect. The oxides which behave as both acidic and basic oxides are called amphoteric oxides. Here $\mathrm{Al_2 O_3}$ is amphoteric oxide and NO is neutral oxide. Hence, A, C and D are incorrect.

Question 78

Chemistry · Structure of Atom · Single correct

The energy of an electron in the first Bohr orbit of hydrogen atom is $-2.18 \times 10^{-18} \, \mathrm{J}$ Its energy in the third Bohr orbit is .

  1. $\frac{1}{9}$ th of the value
  2. $\frac{1}{27}$ of this value
  3. Three times of this value
  4. One third of this value

Answer: (c)

Solution

The energy of an electron in the $n^{th}$ Bohr orbit of a hydrogen atom can be calculated using the formula: $$E_n = \frac{-2.18 \times 10^{-18} Z^2}{n^2}$$ Where $n$ is the principal quantum number of the Bohr orbit. $$E_n \propto \frac{1}{n^2}$$ $$E_n \propto \frac{1}{9}$$ Therefore, the energy of the electron in the third Bohr orbit of a hydrogen atom is three times of this value.

Question 79

Chemistry · Surface Chemistry · Single correct

What happens when a lyophilic sol is added to a lyophobic sol?

  1. Film of lyophilic sol is formed over lyophobic sol
  2. Lyophilic sol is dispersed in lyophobic sol
  3. Film of lyophobic sol is formed over lyophilic sol
  4. Lyophobic sol is coagulated

Answer: (a)

Solution

Film of lyophilic sol is formed over lyophobic sol as lyophilic sol acts as a protective colloid. Lyophobic solutions are unstable in nature. When a lyophilic sol is added to lyophobic sol, stability of lyophobic sol increases due to a protective film of lyophilic sol present over the lyophobic sol.

Question 80

Chemistry · The d-and f-Block Elements · Single correct

The pair of lanthanides in which both elements have high third-ionization energy is:

  1. Dy, Gd
  2. Lu, Yb
  3. Eu, Yb
  4. Eu, Gd

Answer: (c)

Solution

Europium has an atomic number of 63 and a stable electronic configuration of $[\mathrm{Xe}] 4f^7 6s^2$. Ytterbium, on the other hand, has an atomic number of 70 and a stable electronic configuration of $[\mathrm{Xe}] 4f^{14} 6s^2$. Both have high 3rd ionisation energy due to half filled & fully filled configuration respectively.

Question 81

Chemistry · Alcohols, Phenols and Ethers · Numerical

For the given reaction The, total number of possible products formed by tertiary carbocation of A is .

Answer: 5

Solution

There are two tertiary carbocations possible due to rearrangement of hydride or methyl groups. Totally four structural alkene products are formed, out of which one is having chiral centre. Hence, total number of products formed through the formation of carbocation intermediate are 5.

Question 82

Chemistry · Solutions · Numerical

Solution of 12 g of non-electrolyte (A) prepared by dissolving it in 1000 mL of water exerts the same osmotic pressure as that of 0.05 M glucose solution at the same temperature. The empirical formula of A is $\mathrm{CH_2O}$. The molecular mass of A is _______g. (Nearest integer)

Answer: 240

Solution

The pressure which applied externally in the solution side to prevent the osmosis process is known as osmotic pressure. It can be denoted by $\pi$. Since, $\left( \pi_1 \right)_{non electrolyte} = \left( \pi_2 \right)_{glucose}$ $$C_1 \, RT = C_2 \, RT$$ $$\frac{W_1}{M_1} = \frac{W_2}{M_2}$$ Empirical mass of $$\frac{12}{M_1} = 0.05$$ $$M_1 = \frac{12}{0.05} = 240$$

Question 83

Chemistry · Equilibrium · Numerical

25.0 mL of $0.050\,\mathrm{M}\ \mathrm{Ba(NO_3)_2}$ is mixed with 25.0 mL of $0.020\,\mathrm{M}\ \mathrm{NaF}$. $K_{sp}$ of $BaF_2$ is $0.5\times10^{-6}$ at $298\,\mathrm{K}$. The ratio of $\left[\mathrm{Ba^{2+}}\right]\left[\mathrm{F^-}\right]^2$ and $K_{sp}$ is ______.

Answer: 5

Solution

Given: Volume of $\mathrm{Ba(NO_3)_2}$ solution = $25.0 \, \mathrm{mL}$, Concentration of $\mathrm{Ba(NO_3)_2}$ solution = $0.050 \, \mathrm{M}$, Volume of $\mathrm{NaF}$ solution = $25.0 \, \mathrm{mL}$, Concentration of $\mathrm{NaF}$ solution = $0.020 \, \mathrm{M}$. $$[\mathrm{Ba^{2+}}] = \left( \frac{25 \times 0.05}{50} \right) = 0.025 \, \mathrm{M}$$ $$[\mathrm{F^-}] = \left( \frac{25 \times 0.02}{50} \right) = 0.01 \, \mathrm{M}$$ $$[\mathrm{Ba^{2+}}][\mathrm{F^-}] = 25 \times 10^{-7}$$ $$K_{sp} = 0.5 \times 10^{-6} = 5 \times 10^{-7}$$ $$Ratio = \frac{[\mathrm{Ba^{2+}}][\mathrm{F^-}]}{K_{sp}} = \frac{25 \times 10^{-7}}{5 \times 10^{-7}} = 5$$

Question 84

Chemistry · Thermodynamics · Numerical

$\mathrm{A_2 + B_2 \rightarrow 2AB}$. $\Delta H_f = -200 \, \mathrm{kJ \, mol^{-1}}$ AB, $\mathrm{A_2}$ and $\mathrm{B_2}$ are diatomic molecules. If the bond enthalpies of $\mathrm{A_2}$, $\mathrm{B_2}$ and AB are in the ratio $1 : 0.5 : 1$, then the bond enthalpy of $\mathrm{A_2}$ is _______ $\mathrm{kJ \, mol^{-1}}$ (Nearest integer)

Answer: 800

Solution

First write balanced reaction for the formation of one mole of AB with the help of diatomic molecule: $$\frac{1}{2} \mathrm{A_2} + \frac{1}{2} \mathrm{B_2} \rightarrow \mathrm{AB} \Delta H_f = -200 \, \mathrm{kJ/mol}$$ Now, $$\Delta H_{reaction} = \frac{1}{2} \Delta H_{\mathrm{A-A}} + \frac{1}{2} \Delta H_{\mathrm{B-B}} - \Delta H_{\mathrm{AB}} (let, \Delta H_{\mathrm{AB}} = x)$$ $$\frac{1}{2} x + \frac{1}{2} \left(0.5x\right) - x = -200 \Rightarrow \frac{x}{2} + 0.25x - x = -200$$ $$\Rightarrow -0.25x = -200 \Rightarrow x = 800 \, \mathrm{kJ/mol}$$ Bond enthalpy = 800 kJ/mol.

Question 85

Chemistry · Some Basic Concepts of Chemistry · Numerical

An organic compound gives 0.220 g of $\mathrm{CO}_2$ and 0.126 g of $\mathrm{H}_2\mathrm{O}$ on complete combustion. If the % of carbon is 24 then the % of hydrogen is

Answer: 56

Solution

Moles of $\mathrm{CO_2} = \frac{0.22}{44} = \frac{1}{200}$. Then, Mass of $\mathrm{C} = \frac{0.220}{44} \times 12 = 0.06 \, \mathrm{g}$. $\%$ of $\mathrm{C} = \frac{0.06}{W} \times 100 = 24$ (W = Wt. of organic compound) $W = 0.25$ Moles of $\mathrm{H_2O} = \frac{0.126}{18} = 0.007$. Moles of $\mathrm{H} = 0.007 \times 2 = 0.014 \, \mathrm{g}$. $\%$ of Hydrogen = $\frac{0.014 \times 1}{W} \times 100$ $$= \frac{0.014 \times 1}{0.25} \times 100$$ $$= 5.6$$ $$= 56 \times 10^{-1}$$

Question 86

Chemistry · Some Basic Concepts of Chemistry · Numerical

20 $\mathrm{mL}$ of calcium hydroxide was consumed when it was reacted with 10 $\mathrm{mL}$ of unknown solution of $\mathrm{H_2SO_4}$. Also 20 $\mathrm{mL}$ standard solution of 0.5 $\mathrm{M}$ HCl containing 2 drops of phenolphthalein was titrated with calcium hydroxide, the mixture showed pink colour when burette displayed the value of 35.5 $\mathrm{mL}$ whereas the burette showed 25.5 $\mathrm{mL}$ initially. The concentration of $\mathrm{H_2SO_4}$ is $\mathrm{M}$. (Nearest integer)

Answer: 1

Solution

Titration principle is $N_1 V_1 = N_2 V_2$. $N =$ Normality $V =$ Volume of solution $M_1 V_1 n_1 = M_2 V_2 n_2$ $M =$ molarity $n =$ Valence factor of acid or base As pink colour is obtained on consumption of $10 \, \mathrm{ml}$ of $\mathrm{Ca(OH)_2}$, we have $$20 \times 0.5 \times 1 = 10 \times M \times 2$$ Molarity of $\mathrm{Ca(OH)_2} = \frac{10}{20} = \frac{1}{2} M$ Also, moles of $\mathrm{Ca(OH)_2} = \mathrm{mm}$ of $\mathrm{H_2SO_4}$ $$\frac{1}{2} \times 20 = 10 \times M$$ Molarity of $\mathrm{H_2SO_4} = 1 \, \mathrm{M}$

Question 87

Chemistry · States of Matter · Numerical

A certain quantity of real gas occupies a volume of $0.15 \, \mathrm{dm}^3$ at $100 \, \mathrm{atm}$ and $500 \, \mathrm{K}$ when its compressibility factor is $1.07$. Its volume at $300 \, \mathrm{atm}$ and $300 \, \mathrm{K}$ (When its compressibility factor is $1.4$) is _______ $\times 10^{-4} \, \mathrm{dm}^3$ (Nearest integer)

Answer: 392

Solution

The compressibility factor (Z) is given as: $$Z = \frac{PV}{nRT}$$ $$n = \frac{PV}{ZRT}$$ Given $Z_1 = 1.07$, $P_1 = 100 \, atm$, $V_1 = 0.15 \, L$, $T_1 = 500 \, K$ $Z_2 = 1.4$, $P_1 = 300 \, atm$, $V_2 = ?$, $T_2 = 300 \, K$ The relation is: $$\frac{z_1}{z_2} = \frac{P_1 V_1 \times T_2}{T_1 \times P_2 V_2}$$ Substituting the values: $$\frac{1.07}{1.4} = \frac{100 \times 0.15 \times 300}{500 \times 300 \times V_2}$$ Solving for $V_2$: $$V_2 = 0.03925 \, dm^3$$

Question 88

Chemistry · Chemical Kinetics and Nuclear Chemistry · Numerical

$t_{87.5}$ is the time required for the reaction to undergo 87.5$\%$ completion and $t_{50}$ is the time required for the reaction to undergo 50$\%$ completion. The relation between $t_{87.5}$ and $t_{50}$ for a first order reaction is $t_{87.5} = x \times t_{50}$. The value of $x$ is _________. (Nearest integer)

Answer: 3

Solution

The time for completion of the reaction and concentration of reactant relation is as follows, $$A_t = A_0 \times \frac{12.5}{100} = \frac{A_0}{8} \left[ 87.5\% completed \right]$$ $$A_0 \xrightarrow{t_{1/2}} \frac{A_0}{2} \xrightarrow{t_{1/2}} \frac{A_0}{4} \xrightarrow{t_{1/2}} \frac{A_0}{8}$$ $$t_{87.5} = 3t_{1/2}$$ So, $x = 3$

Question 89

Chemistry · Redox Reactions · Numerical

$KMnO_4$ is titrated with ferrous ammonium sulphate hexahydrate in presence of dilute H_2SO_4. Number of water molecules produced for 2 molecules of $KMnO_4$ is

Answer: 68

Solution

By balancing redox reaction: 10[$FeSO_4$. $($NH_4$)_2$ $SO_4$. 6$H_2O$] + 2 $KMnO_4 + 8 $H_2SO_4 $\rightarrow$ 5 $Fe_2(SO_4)_3$ + 2 $MnSO_4$ + 10 $($NH_4$)_2$ $SO_4$ + $K_2SO_4$ + 68 $H_2O$ $$8\mathrm{H^+} + \mathrm{MnO_4^-} + 5 \mathrm{Fe^{+2}} \rightarrow 5 \mathrm{Fe^{+3}} + \mathrm{Mn^{+2}} + 4\mathrm{H_2O}$$ For 2 moles of $\mathrm{MnO_4^-}$, 8 moles of $\mathrm{H_2O}$ are released. 5 moles of Mohr's salt contain 30 moles of $\mathrm{H_2O}$. So, 10 moles of Mohr's salt contain 60 moles of $\mathrm{H_2O}$. So, total moles of $\mathrm{H_2O}$ produced = 68

Question 90

Chemistry · Electrochemistry · Numerical

A metal surface of area $100\,\mathrm{cm^2}$ has to be coated with a nickel layer of thickness $0.001\,\mathrm{mm}$. A current of $2\,\mathrm{A}$ is passed through a solution of $\mathrm{Ni(NO_3)_2}$ for $x$ seconds to obtain the desired coating. The value of $x$ is ________. (Nearest integer) [Given: $\rho_{\mathrm{Ni}}=10\,\mathrm{g\,mL^{-1}}$, molar mass of nickel $=60\,\mathrm{g\,mol^{-1}}$, and $F=96500\,\mathrm{C\,mol^{-1}}$]

Answer: 16

Solution

One equivalent of substance deposited for 96500C (one Faraday). $i \times t$ Columbus of charge can be utilised to get $x$ g of substance. Millimoles of Ni coated $$= \frac{(2x)100}{96500 \times 2}$$ $$= \frac{10x}{965}$$ Mass of Ni $= \left(\frac{x}{965}\right) 600$ $$= \frac{600x}{965} mg$$ Volume $= \frac{60x}{965} \times 10^{-3} cm^3$ $$= 100 \times 10^{-4}$$ $$\Rightarrow x = 0.1608 \times 10^3$$ $$\approx 161$$