JEE Main 29 January 2023 Shift 2 question paper with solutions

JEE Main 29 January 2023 Shift 2: all 90 questions in paper order (Physics, Chemistry, Maths) with the answer key and worked solutions. Free to read; attempt it as a timed 3-hour mock test.

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Physics

Question 1

Physics · Mathematics in Physics · Numerical

In an experiment of measuring the refractive index of a glass slab using travelling microscope in physics lab, a student measures real thickness of the glass slab as 5.25 mm and apparent thickness of the glass slab at 5.00 mm. Travelling microscope has 20 divisions in one cm on main scale and 50 divisions on Vernier scale is equal to 49 divisions on main scale. The estimated uncertainty in the measurement of refractive index of the slab is $\frac{x}{10} \times 10^{-3}$, where $x$ is ________.

Answer: 41

Solution

Given $u = \frac{h}{h'} = \frac{5.25}{5.00}$. Least count $= \frac{1}{20} \, \mathrm{cm} - \frac{49}{50} \cdot \frac{1}{20} \, \mathrm{cm}$ $$= \frac{1}{50} \times \frac{1}{20} \, \mathrm{cm} = 0.01 \, \mathrm{mm}$$ $\ln u = \ln h - \ln h'$ $$\frac{du}{u} = \frac{dh}{h} - \frac{dh'}{h'}$$ $$du = \left[ \frac{0.01}{5.25} + \frac{0.01}{5.00} \right] \frac{5.25}{5.00}$$ $$= \frac{41}{10} \times 10^{-3}$$ Ans. = 41

Question 2

Physics · Physical World, Units and Measurements · Single correct

The equation of a circle is given by $x^2 + y^2 = a^2$, where $a$ is the radius. If the equation is modified to change the origin other than $(0, 0)$, then find out the correct dimensions of $A$ and $B$ in a new equation: $(x - At)^2 + \left( y - \frac{t}{B} \right)^2 = a^2$. The dimensions of $t$ is given as $[T^{-1}]$.

  1. $A = [L^{-1} \, T], \ B = [LT^{-1}]$
  2. $A = (LT), \ B = [L^{-1}T^{-1}]$
  3. $A = [L^{-1}T^{-1}], \ B = [LT^{-1}]$
  4. $A = [L^{-1}T^{-1}], \ B = [LT]$

Answer: (b)

Solution

Given $\left( x - At \right)^2 + \left( y - \frac{t}{B} \right)^2 = a^2$. $[At] = A \times \frac{1}{T} = L$. Therefore, $[A] = T^1 L^1$. $\frac{t}{B}$ is in meters. Therefore, $\frac{1}{T[B]} = L$. Thus, $[B] = T^{-1} L^{-1}$. Correct Ans. (2)

Question 3

Physics · Motion in a Plane · Single correct

An object moves at a constant speed along a circular path in a horizontal plane with centre at the origin. When the object is at $x = +2 \, \mathrm{m}$, its velocity is $-4\hat{j} \, \mathrm{m/s}$. The object's velocity $(v)$ and acceleration $(a)$ at $x = -2 \, \mathrm{m}$ will be

  1. $v = 4\hat{i} \, \mathrm{m/s}, \ a = 8\hat{j} \, \mathrm{m/s^2}$
  2. $v = 4\hat{j} \, \mathrm{m/s}, \ a = 8\hat{i} \, \mathrm{m/s^2}$
  3. $v = -4\hat{j} \, \mathrm{m/s}, \ a = 8\hat{i} \, \mathrm{m/s^2}$
  4. $v = -4\hat{i} \, \mathrm{m/s}, \ a = -8\hat{j} \, \mathrm{m/s^2}$

Answer: (b)

Solution

The centripetal acceleration is given by $a_c = \frac{v^2}{r}$. Substituting the values, we have $$a_c = \frac{4^2}{2} = \frac{16}{2} = 8 \, \mathrm{m/s^2}.$$ The velocity vector is $\vec{V} = 4\hat{j}$. Therefore, the centripetal acceleration vector is $\vec{a_c} = 8\hat{i}$.

Question 4

Physics · Laws of Motion · Numerical

A car is moving on a circular path of radius 600 m such that the magnitudes of the tangential acceleration and centripetal acceleration are equal. The time taken by the car to complete first quarter of revolution, if it is moving with an initial speed of 54 km/hr is $t(1-e^{-\pi/2})$ s. The value of $t$ is.

Answer: 40

Solution

Given $v \frac{dv}{dx} = \frac{v^2}{R}$, we have $\int_{15}^{v} \frac{dv}{v} = \frac{1}{R} \int_{0}^{x} dx$. This gives $v = 15 e^{x/R}$. Then, $\frac{dx}{dt} = 15 e^{x/R}$. Integrating, we have $$\frac{\pi R}{2} \int_{0}^{0} e^{-x/R} dx = 15 \int_{0}^{t_0} dt$$ which results in $$t_0 = 40 \left(1 - e^{-\pi/2}\right).$$

Question 5

Physics · Motion in a Plane · Numerical

A particle of mass 100 g is projected at time $t = 0$ with a speed $20 \, \mathrm{ms}^{-1}$ at an angle $45^\circ$ to the horizontal as given in the figure. The magnitude of the angular momentum of the particle about the starting point at time $t = 2 \, \mathrm{s}$ is found to be $\sqrt{K} \, \mathrm{kgm}^2 / \mathrm{s}$. The value of $K$ is _______. (Take $g = 10 \, \mathrm{ms}^{-2}$)

Answer: 800

Solution

Use $\Delta L = \int_0^t \tau \, dt$ $$L_0 = \int_0^2 mg(v_x t) \, dt$$ $$= mg v_x \frac{t^2}{2} = (0.1)(10)(10\sqrt{2}) \frac{2^2}{2}$$ $$= 20\sqrt{2}$$ $$= \sqrt{800} \, \mathrm{kg} \, \mathrm{m}^2 / \mathrm{s}$$

Question 6

Physics · Laws of Motion · Single correct

The time taken by an object to slide down $45^\circ$ rough inclined plane is $n$ times as it takes to slide down a perfectly smooth $45^\circ$ incline plane. The coefficient of kinetic friction between the object and the incline plane is

  1. $\sqrt{\frac{1}{1-n^2}}$
  2. $\sqrt{1-\frac{1}{n^2}}$
  3. $1+\frac{1}{n^2}$
  4. $1-\frac{1}{n^2}$

Answer: (d)

Solution

Given $a_1 = g \sin \theta = \frac{g}{\sqrt{2}}$. $a_2 = g \sin \theta - K g \cos \theta = \frac{g}{\sqrt{2}} - \frac{K g}{\sqrt{2}}$. $t_2 = n t_1$ and $a_1 t_1^2 = a_2 t_2^2$. $$\frac{g}{\sqrt{2}} t_1^2 = \left( \frac{g}{\sqrt{2}} - \frac{K g}{\sqrt{2}} \right) n^2 t_1^2$$ $K = 1 - \frac{1}{n^2}$. Ans. 4

Question 7

Physics · Laws of Motion · Single correct

Force acts for 20 s on a body of mass 20 kg, starting from rest, after which the force ceases and then body describes 50 m in the next 10 s. The value of force will be :

  1. 40 N
  2. 5 N
  3. 20 N
  4. 10 N

Answer: (b)

Solution

Given the problem, we start with the equation for distance: $$50 = V \times 10$$ Solving for $V$, we get $$V = 5 \, \mathrm{m/s}$$ Using the equation for velocity, $$V = 0 + a \times 20$$ Substituting the value of $V$, $$5 = a \times 20$$ Solving for $a$, we find $$a = \frac{1}{4} \, \mathrm{m/s^2}$$ Using Newton's second law, $$F = ma = 20 \times \frac{1}{4} = 5 \, \mathrm{N}$$

Question 8

Physics · Work, Energy and Power · Single correct

Identify the correct statements from the following: (A) Work done by a man in lifting a bucket out of a well by means of a rope tied to the bucket is negative. (B) Work done by gravitational force in lifting a bucket out of a well by a rope tied to the bucket is negative. (C) Work done by friction on a body sliding down an inclined plane is positive. (D) Work done by an applied force on a body moving on a rough horizontal plane with uniform velocity in zero. (E) Work done by the air resistance on an oscillating pendulum in negative. Choose the correct answer from the options given below:

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

Answer: (a)

Solution

No Solution Available

Question 9

Physics · Gravitation · Single correct

The time period of a satellite of earth is 24 hours. If the separation between the earth and the satellite is decreased to one fourth of the previous value, then its new time period will become.

  1. 4 hours
  2. 6 hours
  3. 12 hours
  4. 3 hours

Answer: (d)

Solution

Given $T^2 \propto R^3$. $$\frac{T_1^2}{T_2^2} = \frac{R_1^3}{R_2^3} \implies \left( \frac{T_1}{T_2} \right)^2 = \left( \frac{R}{\frac{R}{4}} \right)^3$$ Therefore, $$\frac{T_1^2}{T_2^2} = 64$$ Thus, $$T_2^2 = \frac{T_1^2}{64}$$ Therefore, $$T_2 = \frac{24}{8} = 3$$

Question 10

Physics · Mechanical Properties of Fluids · Single correct

A fully loaded boeing aircraft has a mass of $5.4 \times 10^5 \, \mathrm{kg}$. Its total wing area is $500 \, \mathrm{m}^2$. It is in level flight with a speed of $1080 \, \mathrm{km/h}$. If the density of air $\rho$ is $1.2 \, \mathrm{kg \, m^{-3}}$, the fractional increase in the speed of the air on the upper surface of the wing relative to the lower surface in percentage will be $(g = 10 \, \mathrm{m/s^2})$

  1. 16
  2. 6
  3. 8
  4. 10

Answer: (d)

Solution

Given $P_2 A - P_1 A = 5.4 \times 10^5 \times g$. $$P_2 - P_1 = \frac{5.4 \times 10^6}{500} = 5.4 \times 2 \times 10^2 \times 10$$ $$= 10.8 \times 10^3$$ $P_2 + 0 + \frac{1}{2} \rho V_2^2 = P_1 + 0 + \frac{1}{2} \rho V_1^2$ $$P_2 - P_1 = \frac{1}{2} \rho (V_1^2 - V_2^2) = \frac{1}{2} \rho (V_1 - V_2)(V_1 + V_2)$$ $$10.8 \times 10^3 = \frac{1}{2} \times 1.2 (V_1 - V_2) \times 2 \times 3 \times 10^2$$ $$10.8 \times 10 = 3.6 (V_1 - V_2)$$ $$V_1 - V_2 = 30$$ $$\left( \frac{V_1 - V_2}{V} \right) \times 100 = \frac{30}{300} \times 100 = 10\%$$

Question 11

Physics · Mechanical Properties of Fluids · Numerical

A metal block of base area $0.20 \, \mathrm{m}^2$ is placed on a table, as shown in figure. A liquid film of thickness $0.25 \, \mathrm{mm}$ is inserted between the block and the table. The block is pushed by a horizontal force of $0.1 \, \mathrm{N}$ and moves with a constant speed. If the viscosity of the liquid is $5.0 \times 10^{-3} \, \mathrm{Pl}$, the speed of block is _______ $\times 10^{-3} \, \mathrm{m/s}$.

Answer: 25

Solution

Given $|F| = \eta A \frac{\Delta v}{\Delta h}$. $$0.1 = 5 \times 10^{-3} \times 0.2 \times \frac{v}{0.25 \times 10^{-3}}$$ $v = 0.025 \, \mathrm{m/s}$ or $v = 25 \times 10^{-3} \, \mathrm{m/s}$

Question 12

Physics · Thermal Properties of Matter · Single correct

\[ \text{Heat energy of }184\ \text{kJ is given to ice of mass }600\ \text{g} \] \[ \text{at }-12^\circ\text{C}, \text{ Specific heat of ice is } 2222.3\ \text{J kg}^{-1}\,^\circ\text{C}^{-1} \] \[ \text{and latent heat of ice is } 336\ \text{kJ kg}^{-1} \] \[ \text{(A) Final temperature of system will be }0^\circ\text{C.} \] \[ \text{(B) Final temperature of the system will be} \] \[ \text{greater than }0^\circ\text{C.} \] \[ \text{(C) The final system will have a mixture of ice and} \] \[ \text{water in the ratio of }5:1. \] \[ \text{(D) The final system will have a mixture of ice and} \] \[ \text{water in the ratio of }1:5. \] \[ \text{(E) The final system will have water only.} \] \[ \text{Choose the correct answer from the options given} \] \[ \text{below:} \]

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

Answer: (a)

Solution

Given $\Delta Q = 184 \times 10^3$. $m = 0.600 \, \mathrm{kg}$ at $-12^\circ \mathrm{C}$. $S = 222.3 \, \mathrm{J/kg}^\circ \mathrm{C}$. $L = 336 \times 10^3 \, \mathrm{J/kg}$. $Q_1 = 0.600 \times 2222.3 \times 12 = 16000.56 \, \mathrm{J}$. Remaining heat $\Delta Q_1 = 184000 - 16000.56 = 167999.44 \, \mathrm{J}$. For meeting at $0^\circ \mathrm{C}$, $\Delta Q_2 = 0.600 \times 336000 = 201600 \, \mathrm{J}$ needed. Therefore, 100$\%$ ice is not melted. Amount of ice melted: $167999.44 = m \times 336000 = 0.4999 \, \mathrm{kg}$. Therefore, mass of water $= 0.4999 \, \mathrm{kg}$. Mass of ice $= 0.1001$. Therefore, Ratio $= \frac{0.1001}{0.4999} \approx 1 : 5$.

Question 13

Physics · Kinetic Theory · Single correct

At 300 K, the rms speed of oxygen molecules is $\sqrt{\frac{\alpha + 5}{\alpha}}$ times to that of its average speed in the gas. Then, the value of $\alpha$ will be (used $\pi = \frac{22}{7}$)

  1. 32
  2. 28
  3. 24
  4. 27

Answer: (b)

Solution

Given the equation $$\sqrt{\frac{3RT}{M}} = \sqrt{\frac{\alpha + 5}{\alpha}} \sqrt{\frac{8}{\pi} \frac{RT}{M}}$$. Simplifying, we have $$3 = \frac{\alpha + 5}{\alpha} \frac{8}{\pi}$$. Solving for $\alpha$, we find $$\alpha = 28$$.

Question 14

Physics · Oscillations · Numerical

A particle of mass 250 \, $\mathrm{g}$ executes a simple harmonic motion under a periodic force $F = (-25 \, x) \, \mathrm{N}$. The particle attains a maximum speed of $4 \, \mathrm{m/s}$ during its oscillation. The amplitude of the motion is \______ $\mathrm{cm}$.

Answer: 40

Solution

Given $\($ $\frac{1}{4}$ a = -25x $\)$, we have $\($ a = -100x $\)$. Since $\($ $\omega$^2 = 100 $\)$, it follows that $\($ $\omega$ = 10 $\)$. Given $\($ $\omega$ A = 4 $\)$, we find $\($ A = $\frac{4}{10}$ = 0.4 \, $\mathrm{m}$ $\)$. Thus, $\($ A = 40 \, $\mathrm{cm}$ $\)$.

Question 15

Physics · Electric Charges and Fields · Single correct

A point charge $2 \times 10^{-2} \, \mathrm{C}$ is moved from $P$ to $S$ in a uniform electric field of $30 \, \mathrm{NC}^{-1}$ directed along positive x-axis. If coordinates of $P$ and $S$ are $(1, 2, 0) \, \mathrm{m}$ and $(0, 0, 0) \, \mathrm{m}$ respectively, the work done by electric field will be

  1. 1200 mJ
  2. 600 mJ
  3. $-600$ mJ
  4. $-1200$ mJ

Answer: (c)

Solution

The work done by the electric field is given by $\omega_E = q \vec{E} \cdot \vec{S}$. Substituting the given values, we have: $$\omega_E = 2 \times 10^{-2} \left[ 30 \hat{i} \cdot (-\hat{i}) \right]$$ This simplifies to: $$= 2 \times 10^{-2} (-30)$$ Further simplifying: $$= -60 \times 10^{-2}$$ Converting to joules: $$= \frac{-60}{100} = -0.6 \, \mathrm{J}$$ Finally, converting to millijoules: $$= -600 \, \mathrm{mJ}$$

Question 16

Physics · Electric Charges and Fields · Numerical

For a charged spherical ball, electrostatic potential inside the ball varies with $r$ as $V = 2ar^2 + b$. Here, $a$ and $b$ are constant and $r$ is the distance from the center. The volume charge density inside the ball is $-\lambda a \varepsilon$. The value of $\lambda$ is ________. $\varepsilon =$ permittivity of medium.

Answer: 12

Solution

Given $$E = -\frac{dV}{dr} = -4ar \equiv \frac{\rho r}{3 \varepsilon_0}$$ (compare). Result inside uniformly charged solid sphere $$\rho = -12a \varepsilon_0$$ $$\lambda = 12$$

Question 17

Physics · Current Electricity · Single correct

With the help of potentiometer, we can determine the value of emf of a given cell. The sensitivity of the potentiometer is \begin{enumerate} \item[(A)] directly proportional to the length of the potentiometer wire \item[(B)] directly proportional to the potential gradient of the wire \item[(C)] inversely proportional to the potential gradient of the wire \item[(D)] inversely proportional to the length of the potentiometer wire \end{enumerate} Choose the correct option for the above statements:

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

Answer: (b)

Solution

Sensitivity of potentiometer wire is inversely proportional to potential gradient.

Question 18

Physics · Experimental Physics · Numerical

A null point is found at 200 cm in potentiometer when cell in secondary circuit is shunted by $5 \, \Omega$. When a resistance of $15 \, \Omega$ is used for shunting null point moves to 300 cm. The internal resistance of the cell is $\_$$\_$$\_$$\_$ $\Omega$.

Answer: 5

Solution

Given the equation $$\frac{\varepsilon}{r+5} \times 5 = 200x \ldots (1)$$ and $$\frac{\varepsilon \times 15}{r+15} = 300x \ldots (2)$$ solving these equations gives $$\Rightarrow r = 5 \, \Omega$$ Ans. 5

Question 19

Physics · Moving Charges and Magnetism · Single correct

The electric current in a circular coil of four turns produces a magnetic induction 32 T at its centre. The coil is unwound and is rewound into a circular coil of single turn, the magnetic induction at the centre of the coil by the same current will be:

  1. 8T
  2. 4T
  3. 2T
  4. 16T

Answer: (c)

Solution

Given $B = \frac{\mu_0 i}{2R} \times 4$. Then $B' = \frac{\mu_0 i}{2R'}$. Given $R' = 4R$, we have $$B' = \frac{\mu_0 i}{8R}$$ Thus, $$\frac{B'}{B} = \frac{1}{16}$$ Finally, $B' = 2T$.

Question 20

Physics · Moving Charges and Magnetism · Single correct

A square loop of area $25 \mathrm{cm}^2$ has a resistance of $10 \Omega$. The loop is placed in uniform magnetic field of magnitude $40.0 \, \mathrm{T}$. The plane of loop is perpendicular to the magnetic field. The work done in pulling the loop out of the magnetic field slowly and uniformly in $1.0 \, \mathrm{sec}$, will be

  1. $2.5 \times 10^{-3} \, \mathrm{J}$
  2. $1.0 \times 10^{-3} \, \mathrm{J}$
  3. $1.0 \times 10^{-4} \, \mathrm{J}$
  4. $5 \times 10^{-3} \, \mathrm{J}$

Answer: (b)

Solution

Given $\ell = 50 \, \mathrm{cm}$ and $t = 1 \, \mathrm{sec}$. Therefore, $$V = \frac{0.05}{1} = 0.05 \, \mathrm{m/s}.$$ The current $i$ is given by $$i = \frac{40 \times 0.05 \times 0.05}{10} = 0.01 \, \mathrm{A}.$$ The force $F$ is calculated as $$F = B i \ell = 40 \times 0.01 \times 0.05.$$ Thus, $$F = 0.02 \, \mathrm{N}.$$ Therefore, the work $W$ is $$W = 0.02 \times \ell = 0.02 \times 0.05.$$ Finally, $$W = 1 \times 10^{-3} \, \mathrm{J}.$$

Question 21

Physics · Alternating Current · Multiple correct

For the given figures, choose the correct options:

  1. The rms current in circuit (b) can never be larger than that in (a)
  2. The rms current in figure (a) is always equal to that in figure (b)
  3. The rms current in circuit (b) can be larger than that in (a)
  4. At resonance, current in (b) is less than that in (a)

Answer: (a)

Solution

Given a circuit with a resistance of $40 \, \Omega$ and a voltage of $220 \, \mathrm{V}$ at $50 \, \mathrm{Hz}$, the rms current $I_{\mathrm{rms}}$ is calculated as follows: $$I_{\mathrm{rms}} = \frac{220}{40} = 5.5 \, \mathrm{A}$$ In the second circuit, with a resistance of $40 \, \Omega$, an inductance of $50 \, \mathrm{mH}$, and a capacitance of $0.5 \, \mu\mathrm{F}$, $X_L$ is not equal to $X_C$. So rms current in (b) can never be larger than (a).

Question 22

Physics · Alternating Current · Numerical

An inductor of inductance 2 $\mu$$\mathrm{H}$ is connected in series with a resistance, a variable capacitor and an AC source of frequency 7 $\mathrm{kHz}$. The value of capacitance for which maximum current is drawn into the circuit is $\frac{1}{x}$ $\mathrm{F}$, where the value of x is _____. (Take $\pi=\frac{22}{7}$)

Answer: 3872

Solution

Given $\frac{1}{2\pi f C}=2\pi f L$. $C=\frac{1}{4\pi^2f^2L}=\frac{1}{4\times\pi^2\times49\times10^6\times2\times10^{-6}}$ $C=\frac{1}{3872}\,\mathrm{F}$ $x=3872$

Question 23

Physics · Electromagnetic Waves · Single correct

Given below are two statements: Statement I : Electromagnetic waves are not deflected by electric and magnetic field. Statement II : The amplitude of electric field and the magnetic field in electromagnetic waves are related to each other as $E_0 = \sqrt{\frac{\mu_0}{\varepsilon_0}} B_0$ In the light of the above statements, choose the correct answer from the options given below:

  1. Statement I is true but statement II is false
  2. Both Statement I and Statement II are true
  3. Statement I is false but statement II is true
  4. Both Statement I and Statement II are false

Answer: (a)

Solution

Statement-I is correct as EMW are neutral. Statement-II is wrong. $$E_0 = \sqrt{\frac{1}{\mu_0 \varepsilon_0}} B_0$$

Question 24

Physics · Ray Optics and Optical Instruments · Single correct

A scientist is observing a bacteria through a compound microscope. For better analysis and to improve its resolving power he should. (Select the best option)

  1. Increase the wave length of the light
  2. Increase the refractive index of the medium between the object and objective lens
  3. Decrease the focal length of the eye piece
  4. Decrease the diameter of the objective lens

Answer: (a)

Solution

The formula for P is given by $$P = \frac{2 \mu \sin \theta}{1.22 \lambda}.$$

Question 25

Physics · Wave Optics · Numerical

Unpolarised light is incident on the boundary between two dielectric media, whose dielectric constants are 2.8 (medium –1) and 6.8 (medium –2), respectively. To satisfy the condition, so that the reflected and refracted rays are perpendicular to each other, the angle of incidence should be $\tan^{-1}\left(1 + \frac{10}{\theta}\right)^{\frac{1}{2}}$ the value of $\theta$ is _____. (Given for dielectric media, $\mu_r = 1$)

Answer: 7

Solution

Given $\mu_1 = \sqrt{2.8 \times 1} = \sqrt{2.8}$. $\mu_2 = \sqrt{6.8 \times 1} = \sqrt{6.8}$. $\mu_1 \sin i = \mu_2 \cos i$ $\tan i = \frac{\mu_2}{\mu_1} = \sqrt{\frac{6.8}{2.8}}$ $\tan i = \left( \frac{2.8 + 4}{2.8} \right)^{1/2}$ $i = \tan^{-1} \left( 1 + \frac{10}{7} \right)^{1/2}$ $\theta = 7$ Ans.

Question 26

Physics · Dual Nature of Radiation and Matter · Single correct

The ratio of de-Broglie wavelength of an $\alpha$-particle and a proton accelerated from rest by the same potential is $\frac{1}{\sqrt{m}}$, the value of $m$ is

  1. 4
  2. 16
  3. 8
  4. 2

Answer: (c)

Solution

Given $\($ $\frac{\lambda_\alpha}{\lambda_p}$ = $\frac{\frac{h}{\sqrt{2m_\alpha q_\alpha V}}}{\frac{h}{\sqrt{2m_p q_p V}}}$ $\)$. This simplifies to $\($ $\frac{\lambda_\alpha}{\lambda_p}$ = $\sqrt{\frac{1}{8}}$ $\)$ when $\($ m = 8 $\)$. Ans. 3

Question 27

Physics · Nuclei · Single correct

Substance A has atomic mass number 16 and half life of 1 day. Another substance B has atomic mass number 32 and half life of $\frac{1}{2}$ day. If both A and B simultaneously start undergo radio activity at the same time with initial mass 320 g each, how many total atoms of A and B combined would be left after 2 days.

  1. $3.38 \times 10^{24}$
  2. $6.76 \times 10^{24}$
  3. $6.76 \times 10^{23}$
  4. $1.69 \times 10^{24}$

Answer: (a)

Solution

$(N_0)_A = \frac{320}{16} = 20$ moles $(N_0)_B = \frac{320}{32} = 10$ moles$N_A = \frac{(N_0)_A}{(2)^{2/1}} = \frac{20}{4} = 5$ $N_B = \frac{(N_0)_B}{(2)^{2/0.5}} = \frac{10}{2^4} = 0.625$ Total N = 5.625 No. of atoms = 5.625 $\times$ $6.023 \times 10^{23}$ = $3.38 \times 10^{24}$

Question 28

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

For the given logic gates combination, the correct truth table will be

Answer: (b)

Solution

Question 29

Physics · Communication Systems · Single correct

The modulation index for an A.M. wave having maximum and minimum peak to peak voltages of 14 $\mathrm{mV}$ and 6 $\mathrm{mV}$ respectively is:

  1. 1.4
  2. 0.4
  3. 0.2
  4. 0.6

Answer: (b)

Solution

The modulation index $\mu$ is given by the formula: $$\mu = \frac{A_{max} - A_{min}}{A_{max} + A_{min}}.$$ Substituting the given values: $$\mu = \frac{14 - 6}{14 + 6} = 0.4.$$

Question 30

Physics · Current Electricity · Numerical

When two resistance $R_1$ and $R_2$ connected in series and introduced into the left gap of a meter bridge and a resistance of $10 \, \Omega$ is introduced into the right gap, a null point is found at $60 \, \mathrm{cm}$ from left side. When $R_1$ and $R_2$ are connected in parallel and introduced into the left gap, a resistance of $3 \, \Omega$ is introduced into the right-gap to get null point at $40 \, \mathrm{cm}$ from left end. The product of $R_1 \, R_2$ is _____ $\Omega^2$

Answer: 30

Solution

Given $\($ $\frac{R_1 + R_2}{10}$ = $\frac{60}{40}$ = $\frac{3}{2}$ $\Rightarrow$ R_1 + R_2 = 15 $\)$. Now $\($ $\frac{R_1 R_2}{(R_1 + R_2) \times 3}$ = $\frac{40}{60}$ = $\frac{2}{3}$ $\Rightarrow$ R_1 R_2 = 30 $\)$.

Chemistry

Question 31

Chemistry · Structure of Atom · Numerical

Assume that the radius of the first Bohr orbit of hydrogen atom is 0.6 Å. The radius of the third Bohr orbit of He$^+$ is _______ picometer. (Nearest Integer)

Answer: 270

Solution

The radius $r$ is proportional to $\frac{n^2}{Z}$. $$r_{\mathrm{He}^+} = r_{\mathrm{H}} \times \frac{n^2}{Z}$$ Substituting the values, $$r_{\mathrm{He}^+} = 0.6 \times \frac{(3)^2}{2}$$ $$= 2.7 \, \mathrm{\AA}$$ Therefore, $$r_{\mathrm{He}^+} = 270 \, \mathrm{pm}$$

Question 32

Chemistry · The p-Block Elements (Group-13 and 14) · Single correct

Given below are two statements: Statement I : The decrease in first ionization enthalpy from B to Al is much larger than that from Al to Ga. Statement II : The d orbitals in Ga are completely filled. In the light of the above statements, choose the most appropriate answer from the options given below

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

Answer: (b)

Solution

The first ionization energies (as in NCERT) are as follows: B: $801 \, \mathrm{kJ/mol}$ Al: $577 \, \mathrm{kJ/mol}$ Ga: $579 \, \mathrm{kJ/mol}$ Ga: $[\mathrm{Ar}]3d^{10}4s^24p^1$

Question 33

Chemistry · Chemical Bonding and Molecular Structure · Single correct

According to MO theory the bond orders for $\mathrm{O}_2^{2-}$, CO and $\mathrm{NO}^+$ respectively, are

  1. 1, 3 and 3
  2. 1, 3 and 2
  3. 1, 2 and 3
  4. 2, 3 and 3

Answer: (a)

Solution

Theory based.

Question 34

Chemistry · Thermodynamics · Single correct

Which of the following relations are correct? A. $\Delta U = q + p \Delta V$ B. $\Delta G = \Delta H - T \Delta S$ C. $\Delta S = \frac{q_{rev}}{T}$ D. $\Delta H = \Delta U - \Delta nRT$ Choose the most appropriate answer from the options given below:

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

Answer: (b)

Solution

Only (B) and (C) are correct. (B) $G = H - TS$ At constant $T$ $\Delta G = \Delta H - T\Delta S$ (A) First law is given by $\Delta U = Q + W$ If we apply constant $P$ and reversible work, $\Delta U = Q - P\Delta V$ (C) By definition of entropy change $dS = \dfrac{dq_{\mathrm{rev}}}{T}$ At constant $T$ $\Delta S = \dfrac{q_{\mathrm{rev}}}{T}$ (D) $H = U + PV$ For ideal gas $H = U + nRT$ At constant $T$ $\Delta H = \Delta U + \Delta(nRT)$ $\Delta H = \Delta U + nR\Delta T$ Since $\Delta T = 0$ at constant $T$ $\Delta H = \Delta U$ Choose the most appropriate answer from the options given below:

Question 35

Chemistry · Equilibrium · Numerical

At 298 K $\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}, \ K_1 = 4 \times 10^5$ $\mathrm{N_2(g) + O_2(g) \rightleftharpoons 2NO(g)}, \ K_2 = 1.6 \times 10^{12}$ $\mathrm{H_2(g) + \frac{1}{2}O_2(g) \rightleftharpoons H_2O(g)}, \ K_3 = 1.0 \times 10^{-13}$ Based on above equilibria, the equilibrium constant of the reaction, $\mathrm{2NH_3(g) + \frac{5}{2}O_2(g) \rightleftharpoons 2NO(g) + 3H_2O(g)}$ is ___ $\times 10^{-33}$ (Nearest integer)

Answer: 4

Solution

Given the reactions: $$\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}, \ K_1 = 4 \times 10^5 ...(i)$$ $$\mathrm{N_2(g) + O_2(g) \rightleftharpoons 2NO(g)}, \ K_2 = 1.6 \times 10^{12} ...(ii)$$ $$\mathrm{H_2(g) + \frac{1}{2}O_2(g) \rightleftharpoons H_2O(g)}, \ K_3 = 1.0 \times 10^{-13} ...(iii)$$ Using the equation $$(ii) + 3 \times (iii) - (i)$$, we get: $$\mathrm{2NH_3(g) + \frac{5}{2}O_2(g) \rightleftharpoons 2NO(g) + 3H_2O(g)}$$ The equilibrium constant is calculated as: $$k_{\mathrm{eq}} = \frac{k_2 \times k_3^3}{k_1} = \frac{1.6 \times 10^{12} \times (10^{-13})^3}{4 \times 10^5}$$ Simplifying gives: $$= \frac{1.6}{4} \times 10^{-32} = 4 \times 10^{-33}$$

Question 36

Chemistry · Some Basic Concepts of Chemistry · Numerical

The volume of HCl, containing 73 $\mathrm{g \, L^{-1}}$, required to completely neutralise NaOH obtained by reacting 0.69 $\mathrm{g}$ of metallic sodium with water, is _______ $\mathrm{mL}$. (Nearest Integer) (Given : molar Masses of Na, Cl, O, H are 23, 35.5, 16 and 1 $\mathrm{g \, mol^{-1}}$ respectively)

Answer: 15

Solution

Mole of Na $=\dfrac{0.69}{23}=3\times10^{-2}$ $\mathrm{Na + H_2O \rightarrow NaOH + \dfrac{1}{2}H_2}$ By using POAC Moles of NaOH $=3\times10^{-2}$ NaOH reacts with HCl No. of equivalent of NaOH $=$ No. of equivalent of HCl $3\times10^{-2}\times1=\dfrac{73}{36.5}\times V\text{(in L)}\times1$ $V=1.5\times10^{-2}\ \mathrm{L}$ Volume of HCl $=15\ \mathrm{mL}$

Question 37

Chemistry · Redox Reactions · Single correct

An indicator 'X' is used for studying the effect of variation in concentration of iodide on the rate of reaction of iodide ion with $\mathrm{H_2O_2}$ at room temp. The indicator 'X' forms blue colored complex with compound 'A' present in the solution. The indicator 'X' and compound 'A' respectively are

  1. Starch and iodine
  2. Methyl orange and $\mathrm{H_2O_2}$
  3. Starch and $\mathrm{H_2O_2}$
  4. Methyl orange and iodine

Answer: (a)

Solution

The reaction is given by: $$\mathrm{I^- + H_2O_2 \rightarrow I_2 (\mathrm{A}) + H_2O} $$ Then, $\mathrm{I_2}$ reacts with starch as an indicator to form a blue color: $$\mathrm{I_2 + Starch (\mathrm{Indicator}) \rightarrow Blue}$$

Question 38

Chemistry · The s-Block Elements · Numerical

On heating, $\mathrm{LiNO_3}$ gives how many compounds among the following? $\mathrm{Li_2O}$, $\mathrm{N_2}$, $\mathrm{O_2}$, $\mathrm{LiNO_2}$, $\mathrm{NO_2}$

Answer: 3

Solution

The reaction is given by: $$2 \mathrm{LiNO_3} \xrightarrow{\Delta} \mathrm{Li_2O} + 2\mathrm{NO_2} + \frac{1}{2} \mathrm{O_2}$$ Hence three products $\mathrm{Li_2O}$, $\mathrm{NO_2}$, and $\mathrm{O_2}$.

Question 39

Chemistry · Hydrogen · Single correct

Given below are two statements: Statement I : Nickel is being used as the catalyst for producing syn gas and edible fats. Statement II : Silicon forms both electron rich and electron deficient hydrides. 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 correct
  2. Statement I is incorrect but statement II is correct
  3. Both the statements I and II are incorrect
  4. Statement I is correct but statement II is incorrect

Answer: (d)

Solution

Statement–I is correct. Ni is used in Hydrogenation of unsaturated fat to make edible fats. Statement–II is false as hydride of Silicon is electron precise and neither electron deficient nor electron rich.

Question 40

Chemistry · Some Basic Concepts of Chemistry · Single correct

When a hydrocarbon A undergoes combustion in the presence of air, it requires 9.5 equivalents of oxygen and produces 3 equivalents of water. What is the molecular formula of A?

  1. C_8H_6
  2. C_9H_9
  3. C_6H_6
  4. C_9H_6

Answer: (a)

Solution

The balanced chemical equation is: $$\mathrm{C_xH_y} + \left( x + \frac{y}{4} \right) \mathrm{O_2} \rightarrow x \mathrm{CO_2} + \frac{y}{2} \mathrm{H_2O}$$ Solving the equations: $$x + \frac{y}{4} = 9.5$$ $$\frac{y}{2} = 3$$ Thus, $x = 8$ and $y = 6$.

Question 41

Chemistry · Some Basic Concepts of Chemistry · Numerical

When $0.01 \, \mathrm{mol}$ of an organic compound containing $60\%$ carbon was burnt completely, $4.4 \, \mathrm{g}$ of $\mathrm{CO}_2$ was produced. The molar mass of compound is _______ $\mathrm{g \, mol^{-1}}$ (Nearest integer)

Answer: 200

Solution

Let $M$ be the molar mass of the compound (g/mol). The mass of the compound is $0.01 \, M \, \mathrm{gm}$. The mass of carbon is $0.01 \, M \times \frac{60}{100}$. The moles of carbon are given by: $$\frac{0.01 \, M}{12} \times \frac{60}{100}$$ The moles of $\mathrm{CO_2}$ from combustion are: $$\frac{4.4}{44} = moles of carbon$$ Equating the moles of carbon: $$\frac{0.01 \, M}{12} \times \frac{60}{100} = \frac{4.4}{44}$$ Solving for $M$: $$M = \frac{4.4}{44} \times \frac{100}{60} \times \frac{12}{0.01} = 200 \, \mathrm{gm/mol}$$

Question 42

Chemistry · Environmental Chemistry · Single correct

The concentration of dissolved Oxygen in water for growth of fish should be more than $X$ ppm and Biochemical Oxygen Demand in clean water should be less than $Y$ ppm. $X$ and $Y$ in ppm are, respectively.

  1. X Y 6 5
  2. X Y 4 8
  3. X Y 4 15
  4. X Y 6 12

Answer: (a)

Solution

The growth of fish gets inhibited if the concentration of dissolved Oxygen in water is less than 6 ppm and Biochemical Oxygen demand in clean water should be less than 5 ppm.

Question 43

Chemistry · The Solid State · Numerical

A metal M forms hexagonal close-packed structure. The total number of voids in 0.02 mol of it is _______ $\times 10^{21}$ (Nearest integer) (Given $N_A = 6.02 \times 10^{23}$)

Answer: 36

Solution

One unit cell of hcp contains 18 voids. No. of voids in 0.02 mol of hcp $$= \frac{18}{6} \times 6.02 \times 10^{23} \times 0.02$$ $$\approx 3.6 \times 10^{22}$$ $$\approx 36 \times 10^{21}$$

Question 44

Chemistry · Co-ordination Compounds · Single correct

Match List I with List II. Choose the correct answer from the options given below:

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

Answer: (a)

Solution

$(A)$ van't Hoff factor, $i$ $$i = \frac{\text{Normal molar mass}}{\text{Abnormal molar mass}}$$ $(B)$ $k_f =$ Cryoscopic constant $(C)$ Solutions with same osmotic pressure are known as isotonic solutions. $(D)$ Solutions with same composition of vapour over them are called Azeotrope.

Question 45

Chemistry · Electrochemistry · Numerical

The equilibrium constant for the reaction $Zn(s)+Sn^{2+}(aq)\rightleftharpoons Zn^{2+}(aq)+Sn(s)$ is $1\times10^{20}$ at $298\ K$. The magnitude of standard electrode potential of $Sn/Sn^{2+}$ if $E^\circ_{Zn^{2+}/Zn}=-0.76\ V$ is $\underline{\hspace{1cm}}\times10^{-2}\ V$ (Nearest integer) Given $\dfrac{2.303RT}{F}=0.059\ V$

Answer: 17

Solution

$Zn(s)+Sn^{2+}(aq)\rightleftharpoons Zn^{2+}(aq)+Sn(s)$ $\Delta G^\circ=-2.303RT\log_{10}K_{eq}$ $-nFE^\circ_{cell}=-2.303RT\log_{10}K_{eq}$ $E^\circ_{Zn/Zn^{2+}}+E^\circ_{Sn^{2+}/Sn} =\dfrac{0.059}{2}\log_{10}K_{eq}$ $0.76+E^\circ_{Sn^{2+}/Sn} =\dfrac{0.059}{2}\log_{10}10^{20}$ $0.76+E^\circ_{Sn^{2+}/Sn} =\dfrac{0.059\times20}{2}$ $E^\circ_{Sn^{2+}/Sn} =0.59-0.76=-0.17$ $\left|E^\circ_{Sn^{2+}/Sn}\right| =17\times10^{-2}\,V$ Ans. $=17$

Question 46

Chemistry · Chemical Kinetics and Nuclear Chemistry · Fill in the blank

For conversion of compound $A \rightarrow B$, the rate constant of the reaction was found to be $4.6 \times 10^{-5} \, \mathrm{L \, mol^{-1} \, s^{-1}}$. The order of the reaction is ______.

Answer: 2

Solution

As unit of rate constant is $(conc.)^{1-n} time^{-1}$ $$\Rightarrow (\mathrm{L\ mol^{-1}}) \Rightarrow 1-n = -1$$ $$n = 2$$

Question 47

Chemistry · Solutions · Single correct

Match List-I and List-II. Match List-I with List-II \begin{tabular}{|l|l|} \hline \textbf{List-I} & \textbf{List-II} \\ & \\ \hline A. Osmosis & I. Solvent molecules pass through \\ & semi-permeable membrane towards \\ & solvent side. \\ \hline B. Reverse osmosis & II. Movement of charged colloidal \\ & particles under the influence of \\ & applied electric potential towards \\ & oppositely charged electrodes. \\ \hline C. Electro osmosis & III. Solvent molecules pass through \\ & semi-permeable membrane towards \\ & solution side. \\ \hline D. Electrophoresis & IV. Dispersion medium moves \\ & in an electric field. \\ \hline \end{tabular} Choose the correct answer from the options given below:

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

Answer: (b)

Solution

A. Osmosis III B. Reverse osmosis I C. Electro osmosis IV D. Electrophoresis II

Question 48

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

The major component of which of the following ore is sulphide based mineral?

  1. Calamine
  2. Siderite
  3. Sphalerite
  4. Malachite

Answer: (c)

Solution

Calamine: $\mathrm{ZnCO_3}$ Siderite: $\mathrm{FeCO_3}$ Sphalerite: $\mathrm{ZnS}$ Malachite: $\mathrm{CuCO_3} \cdot \mathrm{Cu(OH)_2}$

Question 49

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

Total number of acidic oxides among $\mathrm{N_2O_3}$, $\mathrm{NO_2}$, $\mathrm{N_2O}$, $\mathrm{Cl_2O_7}$, $\mathrm{SO_2}$, $\mathrm{CO}$, $\mathrm{CaO}$, $\mathrm{Na_2O}$ and $\mathrm{NO}$ is .

Answer: 4

Solution

Acidic oxides are $\mathrm{N_2O_3}$, $\mathrm{NO_2}$, $\mathrm{Cl_2O_7}$, $\mathrm{SO_2}$.

Question 50

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

A solution of $\mathrm{CrO_5}$ in amyl alcohol has a....colour

  1. Green
  2. Orange–Red
  3. Yellow
  4. Blue

Answer: (d)

Solution

A solution of $\mathrm{CrO_5}$ in amyl alcohol has a blue colour. So, option (4) is correct.

Question 51

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

The set of correct statements is: (i) Manganese exhibits +7 oxidation state in its oxide. (ii) Ruthenium and Osmium exhibit +8 oxidation in their oxides. (iii) Sc shows +4 oxidation state which is oxidizing in nature. (iv) Cr shows oxidising nature in +6 oxidation state.

  1. (ii) and (iii)
  2. , (ii) and (iv)
  3. and (iii)
  4. (ii), (iii) and (iv)

Answer: (b)

Solution

(i), (ii) and (iv) correct. Manganese exhibits $+7$ oxidation state in its oxide ($\mathrm{Mn_2O_7}$). Ru and Os from $\mathrm{RuO_4}$ and $\mathrm{OsO_4}$ oxide in $+8$ oxidation state. Cr in $+6$ oxidation act is oxidizing. Sc does not show $+4$ oxidation state.

Question 52

Chemistry · Co-ordination Compounds · Single correct

Correct order of spin only magnetic moment of the following complex ions is: (Given At. No. Fe: 26, Co: 27)

  1. $[\mathrm{FeF}_6]^{3-} > [\mathrm{CoF}_6]^{3-} > [\mathrm{Co}(\mathrm{C}_2\mathrm{O}_4)_3]^{3-}$
  2. $[\mathrm{Co}(\mathrm{C}_2\mathrm{O}_4)_3]^{3-} > [\mathrm{CoF}_6]^{3-} > [\mathrm{FeF}_6]^{3-}$
  3. $[\mathrm{FeF}_6]^{3-} > [\mathrm{Co}(\mathrm{C}_2\mathrm{O}_4)_3]^{3-} > [\mathrm{CoF}_6]^{3-}$
  4. $[\mathrm{CoF}_6]^{3-} > [\mathrm{FeF}_6]^{3-} > [\mathrm{Co}(\mathrm{C}_2\mathrm{O}_4)_3]^{3-}$

Answer: (a)

Solution

For $[\mathrm{FeF}_6]^{3-}$: $\mathrm{Fe}^{3+} = 3d^5$, $\Delta_o P$. Number of unpaired $e^- = 0$. Therefore, $\mu = 0 \, \mathrm{BM}$.

Question 53

Chemistry · Co-ordination Compounds · Fill in the blank

The denticity of the ligand present in the Fehling's reagent is _______.

Answer: 4

Solution

Copper tartarate complex. Denticity = 2

Question 54

Chemistry · Hydrocarbons · Single correct

The one giving maximum number of isomeric alkenes on dehydrohalogenation reaction is (excluding rearrangement)

  1. 1-Bromo-2-methylbutane
  2. 2-Bromopropane
  3. 2-Bromopentane
  4. 2-Bromo-3,3-dimethylpentane

Answer: (c)

Solution

The reaction starts with $\mathrm{CH_3 - CH_2 - CH(CH_3) - CH_2 - Br}$ which undergoes a reaction to form $\mathrm{C - C - C = C}$ with a $\mathrm{CH_3}$ group attached. This is labeled as (1). Next, $\mathrm{CH_3 - CH - CH_3}$ with a $\mathrm{Br}$ group undergoes a reaction to form $\mathrm{CH_3CH=CH_2}$, also labeled as (1). Then, $\mathrm{CH_3 - CH_2 - CH_2 - CH(CH_3) - CH_3}$ with a $\mathrm{Br}$ group reacts to form $\mathrm{C - C - C - C - C = C}$ and $\mathrm{C - C - C = C - C}$, with cis and trans isomers, labeled as (3). Finally, $\mathrm{C - C - C - C - C}$ with a $\mathrm{CH_3}$ and $\mathrm{Br}$ group reacts to form $\mathrm{C - C - C - C = C}$ with a $\mathrm{C}$ group attached, labeled as (1).

Question 55

Chemistry · Hydrocarbons · Single correct

Find out the major product for the following reaction.

Answer: (b)

Solution

Question 56

Chemistry · Aldehydes, Ketones and Carboxylic Acids · Single correct

Find out the major products from the following reaction sequence.

Answer: (b)

Solution

The reaction starts with the compound reacting with $NaCN$ to form a cyanohydrin. This intermediate is then treated with $EtOH, H_3O^+$ to form an ester. The ester undergoes a reaction with $MeMgBr$ to form a tertiary alcohol. Further reaction with $MeMgBr$ leads to the formation of a diol.

Question 57

Chemistry · Amines · Single correct

Reaction of propanamide with $\mathrm{Br_2} / \mathrm{KOH} \,(aq)$ produces:

  1. Ethylnitrile
  2. Propylamine
  3. Propanenitrile
  4. Ethylamine

Answer: (d)

Solution

The reaction shown is the Hoffmann Bromamide reaction. It involves the conversion of an amide to an amine with one less carbon atom. The given amide is converted to ethylamine using $\mathrm{Br_2/KOH}$. This reaction results in the removal of the carbonyl group and the formation of an amine.

Question 58

Chemistry · Analytical Chemistry · Single correct

Match List-I and List-II. Choose the correct answer from the options given below:

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

Answer: (c)

Solution

Neoprene: Elastomer Polyester: Fibre Polystyrene: Thermoplastic Urea–Formaldehyde Resin: Thermosetting polymer

Question 59

Chemistry · Chemistry in Everyday Life · Single correct

A doctor prescribed the drug Equanil to a patient. The patient was likely to have symptoms of which disease?

  1. Stomach ulcers
  2. Hyperacidity
  3. Anxiety and stress
  4. Depression and hypertension

Answer: (d)

Solution

Theory based.

Question 60

Chemistry · Biomolecules · Single correct

Following tetrapeptide can be represented as (F, L, D, Y, I, Q, P are one letter codes for amino acids)

  1. FIQY
  2. FLDY
  3. YQLF
  4. PLDY

Answer: (b)

Solution

Hydrolysis of the given tetrapeptide will give the following: Phenylalanine (F), Leucine (L), Aspartic acid (D), Tyrosine (Y).

Maths

Question 61

Maths · Applications of Derivatives · Fill in the blank

Let $\alpha_1$, $\alpha_2$, $\ldots$, $\alpha_7$ be the roots of the equation $x^7 + 3x^5 - 13x^3 - 15x = 0$ and $|\alpha_1| \geq |\alpha_2| \geq \ldots \geq |\alpha_7|$. Then $\alpha_1 \alpha_2 - \alpha_3 \alpha_4 + \alpha_5 \alpha_6$ is equal to _____.

Answer: 9

Solution

Then $\alpha_1 \alpha_2 - \alpha_3 \alpha_4 + \alpha_5 \alpha_6$ is equal to ______. Given equation can be rearranged as $$x(x^6 + 3x^4 - 13x^2 - 15) = 0$$ clearly $x = 0$ is one of the root and other part can be observed by replacing $x^2 = t$ from which we have $$t^3 + 3t^2 - 13t - 15 = 0$$ $$\Rightarrow (t - 3)(t^2 + 6t + 5) = 0$$ So, $t = 3$, $t = -1$, $t = -5$. Now we are getting $x^2 = 3$, $x^2 = -1$, $x^2 = -5$. $$\Rightarrow x = \pm \sqrt{3}, x = \pm i, x = \pm \sqrt{5}i$$ From the given condition $|\alpha_1| \geq |\alpha_2| \geq \ldots \geq |\alpha_7|$ We can clearly say that $|\alpha_7| = 0$ and $|\alpha_6| = \sqrt{5} = |\alpha_5|$ $|\alpha_4| = \sqrt{3} = |\alpha_3|$ and $|\alpha_2| = 1 = |\alpha_1|$ So we can have, $\alpha_1 = \sqrt{5}i$, $\alpha_2 = -\sqrt{5}i$, $\alpha_3 = \sqrt{3}i$, $\alpha_4 = -\sqrt{3}$, $\alpha_5 = i$, $\alpha_6 = -i$. Hence $$\alpha_1 \alpha_2 - \alpha_3 \alpha_4 + \alpha_5 \alpha_6$$ $$= 1 - (-3) + 5 = 9$$

Question 62

Maths · Complex Numbers and Quadratic Equations · Numerical

Let $\alpha=8-14i$, \[ A=\left\{ z\in\mathbb{C}: \frac{\alpha z-\overline{\alpha}\,\overline{z}} {z^2-(\overline{z})^2-112i} =1 \right\} \] and \[ B=\left\{ z\in\mathbb{C}: |z+3i|=4 \right\}. \] Then \[ \sum_{z\in A\cap B}\left(\operatorname{Re}z-\operatorname{Im}z\right) \] is equal to

Answer: 14

Solution

Given $\alpha = 8 - 14i$ and $z = x + iy$. Then, $$az = (8x + 14y) + i(-14x + 8y)$$ $$z + \bar{z} = 2x z - \bar{z} = 2iy$$ Set A: $$\frac{2i(-14x + 8y)}{i(4xy - 112)} = 1$$ $$(x - 4)(y + 7) = 0$$ $$x = 4 or y = -7$$ Set B: $$x^2 + (y + 3)^2 = 16$$ When $x = 4$, $y = -3$ When $y = -7$, $x = 0$ Therefore, $A \cap B = \{4 - 3i, 0 - 7i\}$ So, $$\sum_{z \in A \cap B} (Rez - Imz) = 4 - (-3) + (0 - (-7)) = 14$$

Question 63

Maths · Permutations and Combinations · Single correct

The letters of the word OUGHT are written in all possible ways and these words are arranged as in a dictionary, in a series. Then the serial number of the word TOUGH is :

  1. 89
  2. 84
  3. 86
  4. 79

Answer: (a)

Solution

Let's arrange the letters of OUGHT in alphabetical order. G, H, O, T, U Words starting with G$\_$$\_$$\_$$\_$ $\rightarrow$ 4! H$\_$$\_$$\_$$\_$ $\rightarrow$ 4! O$\_$$\_$$\_$$\_$ $\rightarrow$ 4! TG$\_$$\_$$\_$ $\rightarrow$ 3! TH$\_$$\_$$\_$ $\rightarrow$ 3! TOG$\_$$\_$ $\rightarrow$ 2! TOH$\_$$\_$ $\rightarrow$ 2! TOUGH $\rightarrow$ 1! Total = 89

Question 64

Maths · Permutations and Combinations · Numerical

The total number of 4-digit numbers whose greatest common divisor with 54 is 2, is _____.

Answer: 3000

Solution

N should be divisible by 2 but not by 3. N = (Numbers divisible by 2) - (Numbers divisible by 6) $$N = \frac{9000}{2} - \frac{9000}{6} = 4500 - 1500 = 3000$$

Question 65

Maths · Sequences and Series · Numerical

Let $a_1 = b_1 = 1$ and $a_n = a_{n-1} + (n-1)$, $b_n = b_{n-1} + a_{n-1}$, $\forall \, n \geq 2$. If $S = \sum_{n=1}^{10} \frac{b_n}{2^n}$ and $T = \sum_{n=1}^{8} \frac{n}{2^{n-1}}$, then $2^7(2S - T)$ is equal to .

Answer: 461

Solution

As, $S = \frac{a_1}{2} + \frac{a_2}{2^2} + \ldots + \frac{a_9}{2^9} + \frac{a_{10}}{2^{10}}$. Therefore, $$\frac{S}{2} = \frac{b_1}{2^1} + \frac{b_2}{2^2} + \ldots + \frac{b_9}{2^{10}} + \frac{b_{10}}{2^{11}}.$$ Subtracting, $$S - \frac{S}{2} = \frac{a_1}{2} + \frac{a_2}{2^2} + \ldots + \frac{a_9}{2^9} - \frac{b_{10}}{2^{11}}.$$ Therefore, $$\frac{S}{2} = b_1 - \frac{b_{10}}{2^{10}} + \left( \frac{a_1}{2^2} + \frac{a_2}{2^3} + \ldots + \frac{a_9}{2^9} \right).$$ $$S = b_1 - \frac{b_{10}}{2^{11}} + \left( \frac{a_1}{2} + \frac{a_2}{2^2} + \ldots + \frac{a_9}{2^{10}} \right).$$ Subtracting, $$S = \frac{b_1}{2} - \frac{b_{10}}{2^{11}} + \frac{a_1}{2^2} + \frac{a_9}{2^{10}} + \left( \frac{1}{2^2} + \frac{2}{2^3} + \ldots + \frac{8}{2^9} \right).$$ Therefore, $$S = \frac{a_1 + b_1}{2} - \frac{(b_{10} + 2a_9)}{2^{11}} + \frac{T}{4}.$$ Therefore, $$2S = 2(a_1 + b_1) - \frac{(b_{10} + 2a_9)}{2^9} + T.$$ $$2^7 (2S - T) = 2^8 (a_1 + b_1) - \frac{(b_{10} + 2a_9)}{4}.$$ Given $a_n - a_{n-1} = n - 1$, therefore, $$a_2 - a_1 = 1,$$ $$a_3 - a_2 = 2,$$ $$\vdots$$ $$a_9 - a_8 = 8.$$ Therefore, $$a_9 - a_1 = 1 + 2 + \ldots + 8 = 36.$$ Therefore, $$a_9 = 37 (a_1 = 1).$$ Also, $$b_n - b_{n-1} = a_n - a_{n-1}.$$ Therefore, $$b_{10} - b_1 = a_1 + a_2 + \ldots + a_9$$ $$= 1 + 2 + 4 + 7 + 11 + 16 + 22 + 29 + 37.$$ Therefore, $2^7(2S-T)=2^8(a_1+b_1)-\frac{b_{10}+2a_9}{4}$ $=2^9-\frac{204}{4}$ $=512-51$ $=461$.

Question 66

Maths · Sequences and Series · Numerical

Let $\{a_k\}$ and $\{b_k\}$, $k \in \mathbb{N}$, be two G.P.s with common ratio $r_1$ and $r_2$ respectively such that $a_1 = b_1 = 4$ and $r_1 < r_2$. Let $c_k = a_k + b_k$, $k \in \mathbb{N}$. If $c_2 = 5$ and $c_3 = \frac{13}{4}$ then $$\sum_{k=1}^{\infty} c_k - (12a_6 + 8b_4)$$ is equal to _______.

Answer: 9

Solution

Given that $c_k = a_k + b_k$ and $a_1 = b_1 = 4$. Also $a_2 = 4r_1$, $a_3 = 4r_1^2$, $b_2 = 4r_2$, $b_3 = 4r_2^2$. Now $c_2 = a_2 + b_2 = 5$ and $c_3 = a_3 + b_3 = \frac{13}{4}$. Therefore, $r_1 + r_2 = \frac{5}{4}$ and $r_1^2 + r_2^2 = \frac{13}{16}$. Hence, $r_1 r_2 = \frac{3}{8}$ which gives $r_1 = \frac{1}{2}$ and $r_2 = \frac{3}{4}$. $$\sum_{k=1}^{\infty} c_k - (12a_6 + 8b_4)$$ $$= \frac{4}{1 - r_1} + \frac{4}{1 - r_2} - \left(\frac{48}{32} + \frac{27}{2}\right)$$ $$= 24 - 15 = 9$$

Question 67

Maths · Permutations and Combinations · Single correct

The number of 3 digit numbers, that are divisible by either 3 or 4 but not divisible by 48, is

  1. 472
  2. 432
  3. 507
  4. 400

Answer: (b)

Solution

Total 3 digit number = 900 Divisible by 3 = 300 (Using $\frac{900}{3} = 300$) Divisible by 4 = 225 (Using $\frac{900}{4} = 225$) Divisible by 3 $\&$ 4 = 108, .... (Using $\frac{900}{12} = 75$) Number divisible by either 3 or 4 = 300 + 225 - 75 = 450 We have to remove divisible by 48, 144, 192, ....., 18 terms Required number of numbers = 450 - 18 = 432

Question 68

Maths · Binomial Theorem · Single correct

Let K be the sum of the coefficients of the odd powers of x in the expansion of $(1+x)^{99}$. Let a be the middle term in the expansion of $$\left(2+\frac{1}{\sqrt{2}}\right)^{200}$$. If $$\frac{{^{200}C_{99}K}}{a} = \frac{2^\ell m}{n}$$, where m and n are odd numbers, then the ordered pair $(\ell, n)$ is equal to:

  1. (50, 51)
  2. (51, 99)
  3. (50, 101)
  4. (51, 101)

Answer: (c)

Solution

In the expansion of $(1+x)^{99}$ $=C_{0}+C_{1}x+C_{2}x^{2}+\cdots+C_{99}x^{99}$ $K=C_{1}+C_{3}+\cdots+C_{99}$ $=2^{98}$ Let $a=$ middle term in the expansion of $\left(2+\frac{1}{\sqrt{2}}\right)^{200}$ $T_{200/2+1}$ $={}^{200}C_{100}(2)^{100}\left(\frac{1}{\sqrt{2}}\right)^{100}$ $={}^{200}C_{100}2^{50}$ So, $\frac{{}^{200}C_{99}\times2^{98}}{{}^{200}C_{100}\times2^{50}}$ $=\frac{100\times2^{48}}{101}$ So,$\frac{25}{m}\times2^{50}=\frac{n}{2^{k}}$ $\therefore$ $m,n$ are odd. $(\ell,n)$ become $(50,101)$.

Question 69

Maths · Trigonometric Functions · Single correct

The set of all values of $\lambda$ for which the equation $$\cos^2 2x - 2\sin^4 x - 2\cos^2 x = \lambda$$

  1. [-2, -1]
  2. [-2, -$\frac{3}{2}$]
  3. [-1, -$\frac{1}{2}$]
  4. [$\frac{3}{2}$, -1]

Answer: (d)

Solution

Given $\lambda = \cos^2 x - 2 \sin^4 x - 2 \cos^2 x$. Convert all in to $\cos x$. $$\lambda = (2 \cos^2 x - 1)^2 - 2(1 - \cos^2 x)^2 - 2 \cos^2 x$$ $$= 4 \cos^4 x - 4 \cos^2 x + 1 - 2(1 - 2 \cos^2 x + \cos^4 x) - 2 \cos^2 x$$ $$= 2 \cos^4 x - 2 \cos^2 x + 1 - 2$$ $$= 2 \cos^4 x - 2 \cos^2 x - 1$$ $$= 2 \left[ \cos^4 x - \cos^2 x - \frac{1}{2} \right]$$ $$= 2 \left[ \left( \cos^2 x - \frac{1}{2} \right)^2 - \frac{3}{4} \right]$$ $$\lambda_{\max} = 2 \left[ \frac{1}{4} - \frac{3}{4} \right] = 2 \times \left( -\frac{2}{4} \right) = -1 (max Value)$$ $$\lambda_{\min} = 2 \left[ 0 - \frac{3}{4} \right] = -\frac{3}{2} (Minimum Value)$$ So, Range = $\left$[ -$\frac{3}{2}$, -1 $\right$].

Question 70

Maths · Conic Sections · Numerical

A circle with centre $(2, 3)$ and radius $4$ intersects the line $x + y = 3$ at the points $P$ and $Q$. If the tangents at $P$ and $Q$ intersect at the point $S(\alpha, \beta)$, then $4\alpha - 7\beta$ is equal to .

Answer: 11

Solution

The given line is polar or $P(2, \beta)$ with respect to the given circle $$x^2 + y^2 - 4x - 6y - 3 = 0$$ Chord or contact $$\alpha x + \beta y - 2(x + \alpha) - 3(y + \beta) - 3 = 0$$ $$\Rightarrow (\alpha - 2)x + (\beta - 3)y - (2\alpha + 3\beta + 3) = 0 \ldots (i)$$ But the equation of chord of contact is given as $$x + y - 3 = 0 \ldots (ii)$$ Comparing the coefficients $$\frac{\alpha - 2}{1} = \frac{\beta - 3}{1} = -\left(\frac{2\alpha + 3\beta + 3}{-3}\right)$$ On solving $\alpha = -6$ $\beta = -5$ Now $$4\alpha - 7\beta = 11$$

Question 71

Maths · Conic Sections · Fill in the blank

A triangle is formed by the tangents at the point (2, 2) on the curves $y^2 = 2x$ and $x^2 + y^2 = 4x$, and the line $x + y + 2 = 0$. If $r$ is the radius of its circumcircle, then $r^2$ is equal to _______.

Answer: 10

Solution

Given $S_1 : y^2 = 2x$ and $S_2 : x^2 + y^2 = 4x$. The point $P(2,2)$ is a common point on $S_1$ and $S_2$. $T_1$ is tangent to $S_1$ at $P$, therefore $T_1 : y \cdot 2 = x + 2$. This implies $T_1 : x - 2y + 2 = 0$. $T_2$ is tangent to $S_2$ at $P$, therefore $T_2 : x \cdot 2 + y \cdot 2 = 2(x+2)$. This implies $T_2 : y = 2$. And $L_3 : x + y + 2 = 0$ is the third line. For the triangle $\triangle PQR$, $$PQ = a = \sqrt{20}$$ $$QR = b = \sqrt{8}$$ $$RP = c = 6$$ The area of $\triangle PQR = \Delta = \frac{1}{2} \times 6 \times 2 = 6$. Therefore, $\frac{abc}{4\Delta} = \frac{\sqrt{160}}{4} = \sqrt{10} \implies r^2 = 10$.

Question 72

Maths · Conic Sections · Single correct

If the tangent at a point P on the parabola $y^2 = 3x$ is parallel to the line $x + 2y = 1$ and the tangents at the points Q and R on the ellipse $\frac{x^2}{4} + \frac{y^2}{1} = 1$ are perpendicular to the line $x - y = 2$, then the area of the triangle PQR is:

  1. $\frac{9}{\sqrt{5}}$
  2. $5\sqrt{3}$
  3. $\frac{3}{2}\sqrt{5}$
  4. $3\sqrt{5}$

Answer: (d)

Solution

Given $y^2 = 3x$. Tangent $P(x_1, y_1)$ is parallel to $x + 2y = 1$. Then slope at $P = -\frac{1}{2}$. $$2y \frac{dy}{dx} = 3$$ $$\Rightarrow \frac{dy}{dx} = \frac{3}{2y} = -\frac{1}{2}$$ $$\Rightarrow y_1 = -3$$ Coordinates of $P(3, -3)$. Similarly $Q \left( \frac{4}{\sqrt{3}}, \frac{1}{\sqrt{5}} \right)$, $R \left( -\frac{4}{\sqrt{5}}, -\frac{1}{\sqrt{5}} \right)$. Area of $\triangle APQR$ $$= \frac{1}{2} \begin{vmatrix} 3 & -3 & 1 \\ \frac{4}{\sqrt{5}} & \frac{1}{\sqrt{5}} & 1 \\ -\frac{4}{\sqrt{5}} & \frac{1}{\sqrt{5}} & 1 \end{vmatrix}$$ $$= \frac{1}{2} \left[ 3 \left( \frac{2}{\sqrt{5}} \right) + 3 \left( \frac{8}{\sqrt{5}} \right) + 0 \right] = \frac{30}{2\sqrt{5}} = 3\sqrt{5}$$

Question 73

Maths · Mathematical Reasoning · Single correct

The statement $B \Rightarrow ((\sim A) \lor B)$ is equivalent to

  1. $B \Rightarrow (A \Rightarrow B)$
  2. $A \Rightarrow (A \Rightarrow B)$
  3. $A \Rightarrow ((\sim A) \Rightarrow B)$
  4. $B \Rightarrow ((\sim A) \Rightarrow B)$

Answer: (b)

Solution

\begin{tabular}{|l|l|l|l|} \hline p & q & (p $\rightarrow$ q) & (p $\lor$ q) & (p $\rightarrow$ q) $\land$ (p $\lor$ q) \\ \hline T & T & F & T & T \\ \hline T & F & F & F & T \\ \hline F & T & T & T & T \\ \hline F & F & T & T & T \\ \hline \end{tabular} \begin{tabular}{|l|l|l|l|} \hline A $\Rightarrow$ B & $\neg$ A $\Rightarrow$ B & B $\Rightarrow$ (A $\Rightarrow$ B) & A $\Rightarrow$ (($\neg$ A) $\Rightarrow$ B) & B $\Rightarrow$ (($\neg$ A) $\Rightarrow$ B) \\ \hline T & T & T & T & T \\ \hline F & T & T & T & T \\ \hline T & T & T & T & T \\ \hline T & F & T & T & T \\ \hline \end{tabular}

Question 74

Maths · Statistics · Numerical

Let X = {11, 12, 13, $\ldots$, 40, 41$\}$ and Y = {61, 62, 63, $\ldots$, 90, 91$\}$ be the two sets of observations. If $\bar{x}$ and $\bar{y}$ are their respective means and $\sigma^2$ is the variance of all the observations in X $\cup$ Y, then | $\bar{x}$ + $\bar{y}$ - $\sigma^2$| is equal to .

Answer: 603

Solution

Given $\bar{x} = \frac{1}{31} \sum_{i=11}^{41} i = \frac{11 + 41}{2} = 26$ (31 elements) and $\bar{y} = \frac{1}{31} \sum_{j=61}^{91} j = \frac{61 + 91}{2} = 76$ (31 elements). Combined mean, $\mu = \frac{31 \times 26 + 31 \times 76}{31 + 31} = \frac{26 + 76}{2} = 51$. $$\sigma^2 = \frac{1}{62} \left( \sum_{i=1}^{31} (x_i - \mu)^2 + \sum_{i=1}^{31} (y_i - \mu)^2 \right) = 705$$ Since, $x_i \in X$ are in A.P. with 31 elements & common difference 1, same is $y_i \in y$, when written in increasing order. $$\therefore \sum_{i=1}^{31} (x_i - \mu)^2 = \sum_{i=1}^{31} (y_i - \mu)^2 = 10^2 + 11^2 + \ldots + 40^2$$ $$= \frac{40 \times 41 \times 81}{6} - \frac{9 \times 10 \times 19}{6} = 21855$$ $$\therefore \left| \bar{x} + \bar{y} - \sigma^2 \right| = \left| 26 + 76 - 705 \right| = 603$$

Question 75

Maths · Relations and Functions · Single correct

Let R be a relation defined on $\mathbb{N}$ as $a \, R \, b$ is $2a + 3b$ is a multiple of 5, $a, b \in \mathbb{N}$. Then R is

  1. not reflexive
  2. transitive but not symmetric
  3. symmetric but not transitive
  4. an equivalence relation

Answer: (d)

Solution

Given $a \, R \, a \Rightarrow 5a$ is multiple of $5$. So reflexive. $a \, R \, b \Rightarrow 2a + 3b = 5\alpha$. Now $b \, R \, a$. $$2b + 3a = 2b + \left(\frac{5\alpha - 3b}{2}\right) \cdot 3$$ $$= \frac{15}{2}\alpha - \frac{5}{2}b = \frac{5}{2}(3\alpha - b)$$ $$= \frac{5}{2}(2a + 2b - 2\alpha)$$ $$= 5(a + b - \alpha)$$ Hence symmetric. $a \, R \, b \Rightarrow 2a + 3b = 5\alpha$. $b \, R \, c \Rightarrow 2b + 3c = 5\beta$. Now $$2a + 5b + 3c = 5(\alpha + \beta)$$ $$\Rightarrow 2a + 5b + 3c = 5(\alpha + \beta)$$ $$\Rightarrow 2a + 3c = 5(\alpha + \beta - b)$$ $$\Rightarrow a \, R \, c$$ Hence relation is equivalence relation.

Question 76

Maths · Matrices · Single correct

The set of all values of $t \in \mathbb{R}$, for which the matrix $$\begin{bmatrix} e^t & e^{-t}(\sin t - 2 \cos t) & e^{-t}(-2 \sin t - \cos t) \\ e^t & e^{-t}(2 \sin t + \cos t) & e^{-t}(\sin t - 2 \cos t) \\ e^t & e^{-t} \cos t & e^{-t} \sin t \end{bmatrix}$$ is invertible, is

  1. \quad $\left\{(2k+1)\dfrac{\pi}{2},\,k\in\mathbb{Z}\right\}$
  2. \quad $\left\{k\pi+\dfrac{\pi}{4},\,k\in\mathbb{Z}\right\}$
  3. $\{$ k$\pi$, k $\in$ $\mathbb{Z}$ $\}$
  4. $\mathbb{R}$

Answer: (d)

Solution

If it is invertible, then determinant value $\neq 0$. So, $$\begin{vmatrix} e^t & e^{-t}(\sin t - 2 \cos t) & e^{-t}(-2 \sin t - \cos t) \\ e^t & e^{-t}(2 \sin t + \cos t) & e^{-t}(\sin t - 2 \cos t) \\ e^t & e^{-t} \cos t & e^{-t} \sin t \end{vmatrix} \neq 0$$ $$\Rightarrow e^t \cdot e^{-t} \cdot e^{-t} \begin{vmatrix} 1 & \sin t - 2 \cos t & -2 \sin t - \cos t \\ 1 & 2 \sin t + \cos t & \sin t - 2 \cos t \\ 1 & \cos t & \sin t \end{vmatrix} \neq 0$$ Applying, $R_1 \rightarrow R_1 - R_2$ then $R_2 \rightarrow R_2 - R_3$, we get $$e^{-t} \begin{vmatrix} 0 & -\sin t - \cos t & -3 \sin t + \cos t \\ 0 & 2 \sin t & -2 \cos t \\ 1 & \cos t & \sin t \end{vmatrix} \neq 0$$ By expanding we have, $$e^{-t} \times 1 (2 \sin t \cos t + 6 \cos^2 t + 6 \sin^2 t - 2 \sin t \cos t) \neq 0$$ $$\Rightarrow e^{-t} \times 6 \neq 0$$ for $\forall \ t \in \mathbb{R}$

Question 77

Maths · Matrices · Numerical

Let A be a symmetric matrix such that $|A| = 2$ and $$\begin{bmatrix} 2 & 1 \\ 3 & \frac{3}{2} \end{bmatrix} A = \begin{bmatrix} 1 & 2 \\ \alpha & \beta \end{bmatrix}$$. If the sum of the diagonal elements of $A$ is $s$, then $\frac{\beta s}{\alpha^2}$ is equal to .

Answer: 5

Solution

Now $ac - b^2 = 2$ and $2a + b = 1$ and $2b + c = 2$. Solving all these above equations we get $$\frac{1-b}{2} \times \frac{(2-2b)}{1} - b^2 = 2$$ $$\Rightarrow (1-b)^2 - b^2 = 2$$ $$\Rightarrow 1 - 2b = 2$$ $$\Rightarrow b = -\frac{1}{2} and a = \frac{3}{4} and c = 3$$ Hence $\alpha = 3a + \frac{3b}{2} = \frac{9}{4} - \frac{3}{4} = \frac{3}{2}$ and $\beta = 3b + \frac{3c}{2} = -\frac{3}{2} + \frac{9}{2} = 3$. Also $s = a + c = \frac{15}{4}$. Therefore, $$\frac{\beta s}{\alpha^2} = \frac{3 \times 15}{4 \times \frac{9}{4}} = 5$$

Question 78

Maths · Relations and Functions · Single correct

Consider a function $f : \mathbb{N} \to \mathbb{R}$, satisfying $f(1) + 2f(2) + 3f(3) + \ldots + xf(x) = x(x+1) f(x); \ x \geq 2$ with $f(1)=1$. Then $\frac{1}{f(2022)} + \frac{1}{f(2028)}$ is equal to

  1. 8200
  2. 8000
  3. 8400
  4. 8100

Answer: (d)

Solution

Given for $x \geq 2$ $f(1) + 2f(2) + \ldots + xf(x) = x(x+1)f(x)$ Replace $x$ by $x+1$ $\[$ $\Rightarrow$ x(x+1)f(x) + (x+1)f(x+1) = (x+1)(x+2)f(x+1) $\]$ $\[$ $\Rightarrow$ $\frac{x}{f(x+1)}$ + $\frac{1}{f(x)}$ = $\frac{(x+2)}{f(x)}$ $\]$ $\[$ $\Rightarrow$ x f(x) = (x+1)f(x+1) = $\frac{1}{2}$, x $\geq$ 2 $\]$ $f(2) = \frac{1}{4}, f(3) = \frac{1}{6}$ Now $f(2022) = \frac{1}{4044}$ $f(2028) = \frac{1}{4056}$ So, $\[$ $\frac{1}{f(2022)}$ + $\frac{1}{f(2028)}$ = 4044 + 4056 = 8100 $\]$

Question 79

Maths · Continuity and Differentiability · Single correct

Let f and g be twice differentiable functions on R such that $$f''(x) = g''(x) + 6x$$ $$f'(1) = 4g'(1) - 3 = 9$$ $$f(2) = 3g(2) = 12$$ Then which of the following is NOT true?

  1. $g(-2) - f(-2) = 20$
  2. If $-1 < x < 2$, then $|f(x) - g(x)| < 8$
  3. $|f'(x) - g'(x)| < 6 \Rightarrow -1 < x < 1$
  4. There exists $x_0 \in \left(1, \frac{3}{2}\right)$ such that $f(x_0) = g(x_0)$

Answer: (b)

Solution

Given $$f''(x) = g''(x) + 6x (1)$$ $$f'(1) = 4g'(1) - 3 = 9 (2)$$ $$f(2) = 3g(2) = 12 (3)$$ By integrating (1) $$f'(x) = g'(x) + 6 \frac{x^2}{2} + C$$ At $x = 1$, $$f'(1) = g'(1) + 3 + C$$ $$\Rightarrow 9 = 4 + 3 + C \Rightarrow C = 3$$ $$\therefore \ f'(x) = g'(x) + 3x^2 + 3$$ Again by integrating, $$f(x) = g(x) + \frac{3x^3}{3} + 3x + D$$ At $x = 2$, $$f(2) = g(2) + 8 + 3(2) + D$$ $$\Rightarrow 12 = 4 + 8 + 6 + D \Rightarrow D = -6$$ So, $$f(x) = g(x) + x^3 + 3x - 6$$ $$\Rightarrow f(x) - g(x) = x^3 + 3x - 6$$ At $x = -2$, $$\Rightarrow g(-2) - f(-2) = 20 (Option (1) is true)$$ Now, for $-1 < x < 2$, $$h(x) = f(x) - g(x) = x^3 + 3x - 6$$ $$\Rightarrow h'(x) = 3x^2 + 3$$ $$\Rightarrow h(x) \uparrow$$ So, $h(-1) < h(x) < h(2)$ $$\Rightarrow -10 < h(x) < 8$$ $$\Rightarrow |h(x)| < 10 (option (2) is NOT true)$$

Question 80

Maths · Applications of Derivatives · Fill in the blank

If the equation of the normal to the curve $$y = \frac{x-a}{(x+b)(x-2)}$$ at the point (1, -3) is $x - 4y = 13$, then the value of $a + b$ is equal to _____.

Answer: 4

Solution

Given $\($ y = $\frac{x-a}{(x+b)(x-2)}$ $\)$. At point $\($(1, -3)$\)$, $\[$ -3 = $\frac{1-9}{(1+b)(1-2)}$ $\]$ $\($ $\Rightarrow$ 1-a = 3(1+b) $\)$ $\($ $\ldots$ $\)$ (1) Now, $\($ y = $\frac{x-a}{(x+b)(x-2)}$ $\)$ $\[$ $\Rightarrow$ $\frac{dy}{dx}$ = $\frac{(x+b)(x-2)(1)-(x-a)(2x+b-2)}{(x+b)^2(x-2)^2}$ $\]$ At $\($(1, -3)$\)$ slope of normal is $\($ $\frac{1}{4}$ $\)$ hence $\($ $\frac{dy}{dx}$ = -4 $\)$, So, $\[$ -4 = $\frac{(1+b)(-1)-(1-a)b}{(1+b)^2(-1)^2}$ $\]$ Using equation (1) $\[$ $\Rightarrow$ -4 = $\frac{(1+b)(-1)-3(b+1)b}{(1+b)^2}$ $\]$ $\[$ $\Rightarrow$ -4 = $\frac{(-1)-3b}{(1+b)}$ (b $\neq$ -1) $\]$ $\($ $\Rightarrow$ b = -3 $\)$ So, $\($ a = 7 $\)$ Hence, $\($ a+b = 7-3 = 4 $\)$

Question 81

Maths · Integrals · Single correct

The value of the integral $$\int_{1}^{2} \left( \frac{t^4 + 1}{t^6 + 1} \right) dt$$ is

  1. \[ \quad \tan^{-1}\frac{1}{2} + \frac{1}{3}\tan^{-1}8 - \frac{\pi}{3} \]
  2. \[\quad \tan^{-1}2 - \frac{1}{3}\tan^{-1}8 + \frac{\pi}{3} \]
  3. \[ \quad \tan^{-1}2 + \frac{1}{3}\tan^{-1}8 - \frac{\pi}{3} \]
  4. \[\quad \tan^{-1}\frac{1}{2} - \frac{1}{3}\tan^{-1}8 + \frac{\pi}{3} \]

Answer: (c)

Solution

Given $$I = \int_{1}^{2} \left( \frac{t^4 + 1}{t^6 + 1} \right) \, dt$$ This can be rewritten as $$= \int_{1}^{2} \left( \frac{t^4 + 1 - t^2 + t^2}{(t^2 + 1)(t^4 - t^2 + 1)} \right) \, dt$$ Simplifying, we have $$= \int_{1}^{2} \left( \frac{1}{t^2 + 1} + \frac{t^2}{t^6 + 1} \right) \, dt$$ Further simplifying, $$= \int_{1}^{2} \left( \frac{1}{t^2 + 1} + \frac{1}{3} \frac{3t^2}{(t^3)^2 + 1} \right) \, dt$$ This results in $$= \tan^{-1}(t) + \frac{1}{3} \tan^{-1}(t^3) \bigg|_{1}^{2}$$ Evaluating the integral, $$= (\tan^{-1}(2) - \tan^{-1}(1)) + \frac{1}{3} (\tan^{-1}(2^3) - \tan^{-1}(1^3))$$ Finally, we have $$= \tan^{-1}(2) + \frac{1}{3} \tan^{-1}(8) - \frac{\pi}{3}$$

Question 82

Maths · Integrals · Single correct

The value of the integral $$\int_{1/2}^{2} \frac{\tan^{-1} x}{x} \, dx$$ is equal to

  1. $\pi \log_e 2$
  2. $\frac{1}{2} \log_e 2$
  3. $\frac{\pi}{4} \log_e 2$
  4. $\frac{\pi}{2} \log_e 2$

Answer: (d)

Solution

Given $$I = \int_{1/2}^{2} \frac{\tan^{-1} x}{x} \, dx ...... (i)$$ Put $x = \frac{1}{t}$, $dx = -\frac{1}{t^2} \, dt$ $$I = -\int_{2}^{1/2} \frac{\tan^{-1} \frac{1}{t}}{\frac{1}{t}} \cdot \frac{1}{t^2} \, dt = -\int_{2}^{1/2} \frac{\tan^{-1} \frac{1}{t}}{t} \, dt$$ $$I = \int_{1/2}^{2} \frac{\cot^{-1} t}{t} \, dt = \int_{1/2}^{2} \frac{\cot^{-1} x}{x} \, dx ...... (ii)$$ Add both equations $$2I = \int_{1/2}^{2} \frac{\tan^{-1} x + \cot^{-1} x}{x} \, dx = \frac{\pi}{2} \int_{1/2}^{2} \frac{dx}{x} = \frac{\pi}{2} (\ln 2)_{1/2}^{2}$$ $$= \frac{\pi}{2} \left( \ln 2 - \ln \frac{1}{2} \right) = \pi \ln 2$$ $$I = \frac{\pi}{2} \ln 2$$

Question 83

Maths · Applications of Integrals · Single correct

The area of the region $$A = \left\{ (x, y) : |\cos x - \sin x| \leq y \leq \sin x, 0 \leq x \leq \frac{\pi}{2} \right\}$$

  1. $1 - \frac{3}{\sqrt{2}} + \frac{4}{\sqrt{5}}$
  2. $\sqrt{5} + 2\sqrt{2} - 4.5$
  3. $\frac{3}{\sqrt{5}} - \frac{3}{\sqrt{2}} + 1$
  4. $\sqrt{5} - 2\sqrt{2} + 1$

Answer: (d)

Solution

Given $|\cos x - \sin x| \leq y \leq \sin x$. Intersection point of $\cos x - \sin x = \sin x$ implies $\tan x = \frac{1}{2}$. Let $\psi = \tan^{-1} \frac{1}{2}$. So, $\tan \psi = \frac{1}{2}$, $\sin \psi = \frac{1}{\sqrt{5}}$, $\cos \psi = \frac{2}{\sqrt{5}}$. Area $= \int_{\psi}^{\pi/2} (\sin x - |\cos x - \sin x|) \, dx$ $= \int_{\psi}^{\pi/4} (\sin x - (\cos x - \sin x)) \, dx$ $+ \int_{\pi/4}^{\pi/2} (\sin x - (\sin x - \cos x)) \, dx$ $= \int_{\psi}^{\pi/4} (2 \sin x - \cos x) \, dx + \int_{\pi/4}^{\pi/2} \cos x \, dx$ $= [-2 \cos x - \sin x]_{\psi}^{\pi/4} + [\sin x]_{\pi/4}^{\pi/2}$ $= -\sqrt{2} - \frac{1}{\sqrt{2}} + 2 \cos \psi + \sin \psi + \left(1 - \frac{1}{\sqrt{2}}\right)$

Question 84

Maths · Differential Equations · Single correct

Let $y = y(x)$ be the solution of the differential equation $x \log_e x \frac{dy}{dx} + y = x^2 \log_e x$, $(x > 1)$. If $y(2) = 2$, then $y(e)$ is equal to

  1. $\frac{4 + e^2}{4}$
  2. $\frac{1 + e^2}{4}$
  3. $\frac{2 + e^2}{2}$
  4. $\frac{1 + e^2}{2}$

Answer: (a)

Solution

Given $x \log_e x \frac{dy}{dx} + y = x^2 \log_e x$, $(x > 1)$. $$\Rightarrow \frac{dy}{dx} + \frac{y}{x \ln x} = x$$ Linear differential equation I.F. $= e^{\int \frac{1}{x \ln x} \, dx} = |\ln x|$ Therefore, solution of differential equation $$y |\ln x| = \int x |\ln x| \, dx$$ $$= |\ln x| \frac{x^2}{2} - \int \frac{1}{x} \cdot \frac{x^2}{2} \, dx$$ $$\Rightarrow y |\ln x| = |\ln x| \left( \frac{x^2}{2} \right) - \frac{x^2}{4} + c$$ For constant $y(2) = 2 \Rightarrow c = 1$ So, $y(x) = \frac{x^2}{2} - \frac{x^2}{4 |\ln x|} + \frac{1}{|\ln x|}$ Hence, $y(e) = \frac{e^2}{2} - \frac{e^2}{4} + 1 = 1 + \frac{e^2}{4}$

Question 85

Maths · Vector Algebra · Single correct

If $\vec{a} = \hat{i} + 2\hat{k}$, $\vec{b} = \hat{i} + \hat{j} + \hat{k}$, $\vec{c} = 7\hat{i} - 3\hat{k} + 4\hat{k}$, $\vec{r} \times \vec{b} + \vec{b} \times \vec{c} = \vec{0}$ and $\vec{r} \cdot \vec{a} = 0$ then $\vec{r} \cdot \vec{c}$ is equal to

  1. 34
  2. 12
  3. 36
  4. 30

Answer: (a)

Solution

$$\vec{r}\times\vec{b}-\vec{c}\times\vec{b}=0$$ $$\Rightarrow (\vec{r}-\vec{c})\times\vec{b}=0$$ $$\Rightarrow \vec{r}-\vec{c}=\lambda\vec{b}$$ $$\Rightarrow \vec{r}=\vec{c}+\lambda\vec{b}$$ And given that $$\vec{r}\cdot\vec{a}=0$$ $$\Rightarrow (\vec{c}+\lambda\vec{b})\cdot\vec{a}=0$$ $$\Rightarrow \vec{c}\cdot\vec{a}+\lambda\,\vec{b}\cdot\vec{a}=0$$ $$\Rightarrow \lambda=\frac{-\,\vec{c}\cdot\vec{a}}{\vec{b}\cdot\vec{a}}$$ Now $$\vec{r}\cdot\vec{c}=(\vec{c}+\lambda\vec{b})\cdot\vec{c}$$ $$=\left(\vec{c}-\frac{\vec{c}\cdot\vec{a}}{\vec{b}\cdot\vec{a}}\vec{b}\right)\cdot\vec{c}$$ $$=|\vec{c}|^{2}-\left(\frac{\vec{c}\cdot\vec{a}}{\vec{b}\cdot\vec{a}}\right)(\vec{b}\cdot\vec{c})$$ $$=74-\left(\frac{15}{3}\right)8$$ $$=74-40=34$$

Question 86

Maths · Vector Algebra · Single correct

Let $\vec{a}=4\hat{i}+3\hat{j}$ and $\vec{b}=3\hat{i}-4\hat{j}+5\hat{k}$ and $\vec{c}$ is a vector such that \[ \vec{c}\cdot(\vec{a}\times\vec{b})+25=0, \qquad \vec{c}\cdot(\hat{i}+\hat{j}+\hat{k})=4 \] and projection of $\vec{c}$ on $\vec{a}$ is $1$, then the projection of $\vec{c}$ on $\vec{b}$ equals:

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

Answer: (a)

Solution

Given $\vec{a} \times \vec{b} = 15\hat{i} - 20\hat{j} - 25\hat{k}$. Let $\vec{c} = x\hat{i} + y\hat{j} + z\hat{k}$. Therefore, $15x - 20y - 25z + 25 = 0$. This simplifies to $3x - 4y - 5z = -5$. Also, $x + y + z = 4$. And $\frac{\vec{c} \cdot \vec{a}}{|\vec{a}|} = 1$ implies $4x + 3y = 5$. Therefore, $\vec{c} = 2\hat{i} - \hat{j} + 3\hat{k}$. The projection of $\vec{c}$ or $\vec{b}$ is $\frac{25}{5\sqrt{2}} = \frac{5}{\sqrt{2}}$.

Question 87

Maths · Three Dimensional Geometry · Single correct

Shortest distance between the lines $\($ $\frac{x-1}{2}$ = $\frac{y+8}{-7}$ = $\frac{z-4}{5}$ $\)$ and $\($ $\frac{x-1}{2}$ = $\frac{y-2}{1}$ = $\frac{z-6}{-3}$ $\)$ is

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

Answer: (b)

Solution

Given $\($ $\frac{x-1}{2}$ = $\frac{y+8}{-7}$ = $\frac{z-4}{5}$ $\)$ and $\($ $\frac{x-1}{2}$ = $\frac{y-2}{1}$ = $\frac{z-6}{-3}$ $\)$. $\($ $\mathbf{p}$ = 2$\hat{i}$ - 7$\hat{j}$ + 5$\hat{k}$, $\mathbf{q}$ = 2$\hat{i}$ + $\hat{j}$ - 3$\hat{k}$ $\)$. $\($ $\mathbf{a}$ = $\hat{i}$ - 8$\hat{j}$ + 4$\hat{k}$ $\)$ and $\($ $\mathbf{b}$ = $\hat{i}$ + 2$\hat{j}$ + 6$\hat{k}$ $\)$. Calculate $\($ $\mathbf{p}$ $\times$ $\mathbf{q}$ $\)$: $$ \mathbf{p} \times \mathbf{q} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k} \\ 2 & -7 & 5 \\ 2 & 1 & -3 \end{vmatrix} $$ $$ = \hat{i}(16) - \hat{j}(-16) + \hat{k}(16) $$ $$ = 16(\hat{i} + \hat{j} + \hat{k}) $$ Calculate $\($ d = $\frac{|(\mathbf{a} - \mathbf{b}) \cdot (\mathbf{p} \times \mathbf{q})|}{|\mathbf{p} \times \mathbf{q}|}$ $\)$: $$ d = \frac{|(-10\hat{j} - 2\hat{k}) \cdot 16(\hat{i} + \hat{j} + \hat{k})|}{16\sqrt{3}} $$ $$ = \frac{|-12|}{\sqrt{3}} = 4\sqrt{3} $$

Question 88

Maths · Three Dimensional Geometry · Single correct

The plane $2x - y + z = 4$ intersects the line segment joining the points $A(a, -2, 4)$ and $B(2, b, -3)$ at the point $C$ in the ratio $2 : 1$ and the distance of the point $C$ from the origin is $\sqrt{5}$. If $ab < 0$ and $P$ is the point $(a - b, b, 2b - a)$ then $CP^2$ is equal to:

  1. $\($ $\frac{17}{3}$ $\)$
  2. $\($ $\frac{16}{3}$ $\)$
  3. $\($ $\frac{73}{3}$ $\)$
  4. $\($ $\frac{97}{3}$ $\)$

Answer: (a)

Solution

Given points A(a, -2, 4), B(2, b, -3). The ratio AC : CB = 2 : 1. Therefore, $$C \equiv \left( \frac{a+4}{3}, \frac{2b-2}{3}, \frac{-2}{3} \right)$$ C lies on the line $2x - y + 2 = 4$. Thus, $$\frac{2a+8}{3} - \frac{2b-2}{3} - \frac{2}{3} = 4$$ This implies $a - b = 2 \ldots (1)$ Also, $OC = \sqrt{5}$ Therefore, $$\left( \frac{a+4}{3} \right)^2 + \left( \frac{2b-2}{3} \right)^2 + \frac{4}{9} = 5 \ldots (2)$$ Solving equations (1) and (2), $$(b+6)^2 + (2b-2)^2 = 41$$ This implies $$5b^2 + 4b - 1 = 0$$ Thus, $b = -1$ or $\frac{1}{5}$ Therefore, $a = 1$ or $\frac{11}{5}$ But $ab < 0$ implies $(a, b) = (1, -1)$ Thus, $$C \equiv \left( \frac{5}{3}, -\frac{4}{3}, -\frac{2}{3} \right), \ P \equiv (2, -1, -3)$$ Finally, $$CP^2 = \frac{1}{9} + \frac{1}{9} + \frac{49}{9} = \frac{51}{9} = \frac{17}{3}$$

Question 89

Maths · Three Dimensional Geometry · Single correct

If the lines $\frac{x-1}{1} = \frac{y-2}{2} = \frac{z+3}{1}$ and $\frac{x-a}{2} = \frac{y+2}{3} = \frac{z-3}{1}$ intersects at the point P, then the distance of the point P from the plane $z = a$ is:

  1. 16
  2. 28
  3. 10
  4. 22

Answer: (b)

Solution

Point on $L_1 \equiv (\lambda + 1, 2\lambda + 2, \lambda - 3)$ Point on $L_2 \equiv (2\mu + a, 3\mu - 2, \mu + 3)$ $\lambda - 3 = \mu + 3 \Rightarrow \lambda = \mu + 6 \ldots (1)$ $2\lambda + 2 = 3\mu - 2 \Rightarrow 2\lambda = 3\mu - 4 \ldots (2)$ Solving, (1) and (2) $\Rightarrow \lambda = 22 and \mu = 16$ $\Rightarrow P \equiv (23, 46, 19)$ $\Rightarrow a = -9$

Question 90

Maths · Probability · Single correct

Let \(S=\{w_1,w_2,\ldots\}\) be the sample space associated with a random experiment. Let \[ P(w_n)=\frac{P(w_{n-1})}{2}, \qquad n\ge 2. \] Let \[ A=\{2k+3\ell \,;\, k,\ell\in\mathbb{N}\} \] and \[ B=\{w_n \,;\, n\in A\}. \] Then \(P(B)\) is equal to

  1. $\frac{3}{32}$
  2. $\frac{3}{64}$
  3. $\frac{1}{16}$
  4. $\frac{1}{32}$

Answer: (b)

Solution

Let $P(w_1)=\lambda$. Then $P(w_2)=\frac{\lambda}{2}, \ldots, P(w_n)=\frac{\lambda}{2^{n-1}}$. As $$ \sum_{k=1}^{\infty} P(w_k)=1 \implies \frac{\lambda}{1-\frac{1}{2}}=1 \implies \lambda=\frac{1}{2}. $$ So, $$ P(w_n)=\frac{1}{2^n}. $$ Also, $$ A=\{2k+3\ell;\,k,\ell\in\mathbb{N}\} =\{5,7,8,9,10,\ldots\}. $$ Hence, $$ B=\{w_n:n\in A\} =\{w_5,w_7,w_8,w_9,w_{10},w_{11},\ldots\}. $$ Observe that $$ A=\mathbb{N}\setminus\{1,2,3,4,6\}. $$ Therefore, $$ P(B) =1-\left[P(w_1)+P(w_2)+P(w_3)+P(w_4)+P(w_6)\right] $$ $$ =1-\left[ \frac{1}{2} +\frac{1}{4} +\frac{1}{8} +\frac{1}{16} +\frac{1}{64} \right] $$ $$ =1-\frac{32+16+8+4+1}{64} =\frac{3}{64}. $$