NSEJS 2021 Question Paper

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Question 1

The axes of a coordinate system $\mathrm{S}_{2}$ are inclined at an angle $\theta$ to those of another coordinate system $\mathrm{S}_{1}$. The origins of both the systems are coinciding. A particle $\mathrm{P}_{1}$ at rest in system $\mathrm{S}_{1}$, starts from point ($-2,0$) and travels along positive direction of $\mathrm{X}_{1}$ axis with uniform acceleration of $1.25 \mathrm{ m} / \mathrm{s}^{2}$ for 4 s and stops. In system $\mathrm{S}_{2}$, particle $\mathrm{P}_{2}$, starts from rest from the origin and travels for 2 s along positive direction of $\mathrm{X}_{2}$ axis with uniform acceleration $5 \mathrm{ m} / \mathrm{s}^{2}$ and stops. If the final distance between $P_{1}$ and $P_{2}$ is 6 m , then the angle between $+\mathrm{Y}_{1}$ axis and $+\mathrm{X}_{2}$ axis is

(a) $36.8^{\circ}$
(b) $53.2^{\circ}$
(c) $106.8^{\circ}$
(d) $126.8^{\circ}$

Question 2

The variation of a certain physical parameter $Z$ with variable $u$ is given by the relation $\mathrm{Z}=A\left(\frac{R}{R+u}\right)^{3}$, where $R$ and $A$ are constants and the maximum value of $u \ll R$. Then to find $R$, a student plots a graph of variation of $Z$ ( Y axis) against $u$ ( X axis). The graph is a

(a) straight line passing through origin and slope $=\frac{R}{3}$
(b) straight line with intercept $\frac{3 A}{2}$ and slope $=-\frac{R}{3 A}$
(c) straight line with intercept $A$ and slope $=-\frac{3 A}{R}$
(d) straight line with intercept $-\frac{A}{2}$ and slope $=-3 R$

Question 3

A submarine $S_{1}$ is parked at a depth of 200 m in an ocean on earth. Assume oceans exist on Mars. At about what depth a submarine $\mathrm{S}_{2}$ has to be parked in an ocean on Mars so that $\mathrm{S}_{2}$ will experience same pressure as that of $\mathrm{S}_{1}$ ? Acceleration due to gravity on Mars is $3.7 \mathrm{ m} / \mathrm{s}^{2}$. (Assume that sea water density on Earth and Mars is same, $\rho=1.03 \times 10^{3} \mathrm{ kg} / \mathrm{m}^{3}$ )

(a) 158 m
(b) 435 m
(c) 530 m
(d) 616 m

Question 4

In an oscillating system, damping results in dissipation of the stored energy. The following figure shows the variation of displacement x with time t for an oscillating system. Which of the following statements best describes this physical phenomenon.

(a) Oscillatory motion of an object without damping
(b) Oscillatory motion of an object with damping such that time measurement was started when the system was at the mean position.
(c) Oscillatory motion of an object with damping with decreasing time period.
(d) Oscillatory motion of an object with damping such that time measurement was started when the system had maximum potential energy.

Question 5

In the adjacent circuit, the galvanometer $G$ does not show any deflection. If $R=2 \Omega$, the current drawn from the cell is

(a) 1 A
(b) 9 A
(c) 4 A
(d) $\frac{9}{4} \mathrm{ A}$

Question 6

'Gear' is a mechanical system used to transfer mechanical and rotary motion from one mechanical system to another. As shown in the figure below the driving wheel A drives the driven wheel B without slipping and thus forms the gear system. The wheel A has 16 teeth and B has 24 teeth. Wheel B has a projection (shown by white ring in Fig. 1 and also in the side view of Fig. 2) of radius $\frac{14}{11} \mathrm{ cm}$.

A long massless, inextensible string can be wound / unwound over this circular projection. A mass $m$ is attached to the free end of this long string. If the wheel A makes 6 revolutions per second in the clockwise direction, without slipping, then in $\frac{1}{2}$ second the potential energy of the mass $m$ in CGS unit

(a) increases by $32 m g$
(b) decreases by 32 mg
(c) increases by 16 mg
(d) decreases by 16 mg

Question 7

Canopus is the second brightest star in the night sky. It is about 300 light years away. The energy is produced inside the star through nuclear reactions. If we receive $5.0 \times 10^{-8} \mathrm{ W} / \mathrm{m}^{2}$ energy from Canopus, how much mass does it lose per second?

(a) $1.70 \times 10^{-6} \mathrm{ kg}$
(b) $1.91 \times 10^{9} \mathrm{ kg}$
(c) $5.62 \times 10^{13} \mathrm{ kg}$
(d) $6.34 \times 10^{31} \mathrm{ kg}$

Question 8

An average human adult radiates about 100 W energy mainly in infra-red region of the electromagnetic spectrum. 50 persons are sitting in a hall with an air conditioning system which is $50 %$ efficient. How much electricity must be used to maintain temperature of the hall at $25^{\circ} \mathrm{C}$ for 4 hours?

(a) 5 units
(b) 10 units
(c) 20 units
(d) 40 units

ANY NUMBER OF OPTIONS 4, 3, 2 or 1 MAY BE CORRECT IN THE FOLLOWING QUESTIONS.

Question 9

According to Einstein's theory, light can be assumed to be in the form of a large number of discrete energy packets called 'photons'. In case of light of frequency $v$, each photon carries energy $E=h v$. In a certain surgical procedure a surgeon uses LASER beam of wavelength 650 nm in pulses of 30.0 ms duration. The average power of each pulse is 0.6 W . Here h is Planck's constant. Then

(a) the frequency of this LASER photon is $4.6 \times 10^{14} \mathrm{ Hz}$
(b) the energy in each pulse is $1.1 \times 10^{17} \mathrm{eV}$
(c) energy of one photon is $3.1 \times 10^{-19} J$
(d) number of photons in each pulse is $5.9 \times 10^{16}$

Question 10

In the following circuit, $\mathrm{R}_{1}=6 \Omega, \mathrm{R}_{2}=12 \Omega, \mathrm{ V}=16 \mathrm{ V}$. The currents $\mathrm{I}_{1}$ and $\mathrm{I}_{2}$ flow through the resistances $\mathrm{R}_{1}$ and $\mathrm{R}_{2}$ respectively

(a) power generated across $\mathrm{R}_{1}$ is 42.6 watt
(b) the ratio of $\frac{I_{1}}{I_{2}}=2$
(c) total current drawn from the cell is 4 ampere
(d) as $R_{2}=2 R_{1}$, the voltage across $R_{2}$ will be twice the voltage across $\mathrm{R}_{1}$

Question 11

A glass plate of uniform thickness $t$ and refractive index $\mu$ is as shown in the diagram. AB is the incident ray and FG is the emergent ray. The angles of incidence and refraction are $i$ and $r$ respectively. The perpendicular distance $\mathrm{FC}=x$ between the incident and the emergent rays is called the lateral shift. Then

(a) $x=t\left(\sin i-\frac{\cos i \sin r}{\cos r}\right)$
(b) $x$ depends on refractive index $\mu$
(c) $x$ is independent of the wavelength $\lambda$ of light
(d) Maximum value of $x=t$ when $i$ is close to $90^{\circ}$
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