Work, Energy & Power PYQs Set 5 (PDF)

Set 5 of 9 · Questions 121-150 of 248

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Mere Teacher · Previous Year Questions NEET Physics · Work, Energy & Power · Set 5 (Q121-150)
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121. $Potential energy as a function of r is given by U = \frac{A}{r ^{10}} - \frac{B}{r ^{5}}, where r is the interatomic distance, A and B are positive constants. The equilibrium distance between the two atoms will be:$ (1) $(\frac{A}{B})^{\frac{1}{5}}$ (2) $(\frac{B}{A})^{\frac{1}{5}}$ (3) $(\frac{2 A}{B})^{\frac{1}{5}}$ (4) $(\frac{B}{2 A})^{\frac{1}{5}}$ 122. $The potential energy of a long spring when stretched by 2 cm is U . Ifthe spring is stretched by 8 cm the potential energy stored in it i$ (1) $UI4$ (2) $4U$ (3) $8U$ (4) $16U$ 123. $If the linear momentum of a body is increased by 50 %, then the kinetic energy of that body increases by$ (1) $100 %$ (2) $125 %$ (3) $225 %$ (4) $25 %$ 124. $Water falls from a height of 60 m at the rate of 15 kg / s to operate a turbine. The losses due to frictional force are 10 % of the input energy. How much power is generated by the turbine? (g = 10 m / s^{2}) [NEET 2021]$ (1) $10.2 kW$ (2) $8.1 kW$ (3) $12.3 kW$ (4) $7.0 kW$ 125. $A particle is projected at 6 0^{º} to the horizontal with a kinetic energy K. The kinetic energy at the highest point is$ (1) $K$ (2) $zero$ (3) $K/4$ (4) $K/2$ 126. $A body of mass 2 kg begins to move under the action of a time dependent force given by F = (6 t i + 6 t^{2} j) N . The power developed by the force at the time t is given by:$ (1) $(6 t^{4} + 9 t^{5}) W$ (2) $(3 t^{3} + 6 t^{5}) W$ (3) $(9 t^{5} + 6 t^{3}) W$ (4) $(9 t^{3} + 6 t^{5}) W$ 127. $A force of 10 N acting at an angle on a particle produces a displacement of (3 ı - 4 ȷ) m . Due to this force, if the kinetic energy of the particle is decreased by 25 joule, then the angle between the force and the displacement is$ (1) $cos^{- 1} (\frac{1}{3})$ (2) $30^{\circ}$ (3) $120^{\circ}$ (4) $cos^{- 1} (\frac{3}{4})$ 128. $The potential energy of an object is U (xx) = (5 x^{2} - 4 x^{3}) J, where x is the position in meter. The position at which the force becomes zero is$ (1) $\frac{1}{2} m$ (2) $\frac{5}{6} m$ (3) $\frac{1}{3} m$ (4) $\frac{2}{3} m$ 129. $A person of mass M is, sitting on a swing of length L and swinging with an angular amplitude θ_{0} . If the person stands up when the swing passes through its lowest point, the work done by him, assuming that his center of mass moves by a distance l (l << L) is close to:$ (1) $mgl (1 - θ_{0}^{2})$ (2) $mgl (1 + θ_{0}^{2})$ (3) $mgl$ (4) $Mgl (1 + \frac{θ _{0}^{2}}{2})$ 130. $Two bodies of masses of 1g and 4g are moving with equal kinetic energies. The ratio of the magnitudes of their linear momenta is$ (1) $4 : 1$ (2) $2 : 1$ (3) $1 : 2$ (4) $1 : 16$ 131. $If kinetic energy of a body is increased by 300% then percentage change in momentum will be$ (1) $100%$ (2) $150%$ (3) $265%$ (4) $73.2%.$ 132. $A particle moves from (1, 0, 3) to the point (- 3, 4, 5), when a force F = i + 5 k acts on it. Amount of work done in joules is$ (1) $14$ (2) $10$ (3) $6$ (4) $15$ 133. $Two springs A and B fixed at the top and are stretched by 8 cm and 16 cm respectively, when loads of 20 N and 10 N are suspended at the lower ends. The ratio of the spring constants of the springs A and B is$ (1) $1 : 1$ (2) $2 : 1$ (3) $3 : 1$ (4) $4 : 1$ 134. $A body, constrained to move in y ‐direction, is subjected to a force given by F = (- 2 i + 15 j + 6 k) N . The work done by this force in moving the body through a distance of 10 j m along y ‐axis, is$ (1) $150 J$ (2) $20 J$ (3) $190 J$ (4) $160 J.$ 135. $A bullet of mass 50 g is fired with a speed 100 m / s on a plywood and emerges with 40 m / s . The percentage loss of kinetic energy is:$ (1) $84 %$ (2) $16 %$ (3) $32 %$ (4) $44 %$ 136. $A car of mass 1000 kg having a velocity of 10 ms^{- 1} collides a horizontally mounted spring. If the spring constant is 4000 Nm^{- 1}, then the maximum compression of the spring is$ (1) $25 m$ (2) $15 m$ (3) $5 m$ (4) $10 m$ 137. $Consider a drop of rain water having mass 1 g falling from a height of 1 km. It hits the ground with a speed of 50 m/s. Take 'g' constant with a value 10 m/ s^{2} . The work done by the (i) gravitational force and the (ii) resistive force of air is:$ (1) $(i) - 10 J (ii) - 8.25 J$ (2) $(i) 1.25 J (ii) - 8.25 J$ (3) $(i) 100 J (ii) 8.75 J$ (4) $(i) 10 J (ii) - 8.75 J$ 138. $The kinetic energy of a body of mass 4 kg and momentum 6 Ns will be$ (1) $3.5 J$ (2) $5.5 J$ (3) $2.5 I$ (4) $4.5 J$ 139. $A porter lifts a heavy suitcase of mass 80kg and at the destination lowers it down by a distance of 80cm with a constant velocity. Calculate the work done by the porter in lowering the suitcase. (take g=9. 8 m s^{- 2})$ (1) $-62720.0J$ (2) $-627.2J$ (3) $+627.2J$ (4) $784.0J$ 140. $A body of mass 1 kg is thrown upwards with a velocity 20 \frac{m}{s} . It momentarily comes to rest after attaining a height of 18 m . How much energy is lost due to air friction? (g = \frac{10 m}{s ^{2}})$ (1) $30 J$ (2) $40 J$ (3) $10 J$ (4) $20 J$ 141. $A bomb of mass 16 kg explodes into two pieces of masses 4 kg and 12 kg . The velocity of the 12 kg mass is 4 ms^{- 1} . The kinetic energy of the second piece is$ (1) $144 J$ (2) $192 J$ (3) $96 J$ (4) $288 J$ 142. $A bead of mass 400 g is moving along a straight line under a force that delivers a constant power 1.2 W to the bead. If the bead is initially at rest, the speed it attains after 6 sec in ms^{- 1}$ (1) $5$ (2) $4$ (3) $6$ (4) $3$ 143. $One coolie takes 1 minute to raise a suitcase through a height of 2 m but the second coolie takes 30 s to raise the same suitcase to the same height. The powers of two coolies are in the ratio (NEET2013)$ (1) $1 : 3$ (2) $2: 1$ (3) $3 : 1$ (4) $1 : 2$ 144. $The heart of a man pumps 5 liters of blood through the arteries per minute at a pressure of 150 mm of mercury. If the density of mercury be 13. 6 \times 1 0^{3} kg / m^{3} and g = 10 m / s^{2} then the power (in watt) is$ (1) $3.0$ (2) $1.50$ (3) $1.70$ (4) $2.35$ 145. $An athlete in the Olympic games covers a distance of 100 m in 10 s. His kinetic energy can be estimated to be in the range$ (1) $2 \times 1 0^{5} J - 3 \times 1 0^{5} J$ (2) $20,000 J - 50,000 J$ (3) $2,000 J - 5,000 J$ (4) $200 J - 500 J$ 146. $When a long spring is stretched by 2 cm, its potential energy is U . If the spring is stretched by 10 cm, the potential energy stored in it will be$ (1) $U /5$ (2) $5 U$ (3) $10 U$ (4) $2 5 U$ 147. $The work done in moving a body of mass 2 kg to a height of 4 m from the surface of the earth is (Acceleration due to gravity = 10 ms^{- 2})$ (1) $10 J$ (2) $20 J$ (3) $40 J$ (4) $80 J$ 148. $Which of the following is a incorrect statement?$ (1) $Work done by conservative force is equal to negative change in potential energy.$ (2) $Total energy of system is always conserved.$ (3) $Work done by non-conservative force in a closed path is equal to zero.$ (4) $In stable equilibrium, the potential energy is minimum.$ 149. $A motor pump lifts 6 tonnes of water from a well of depth 25 m to the first floor of height 35 m from the ground floor in 20 minutes. The power of the pump (in kW) is (g = 10 m s^{- 2})]$ (1) $6$ (2) $1.5$ (3) $12$ (4) $3$ 150. $A rifle bullet loses (\frac{1}{25}) th of its velocity in passing through a plank. The least number of such planks required just to stop the bullet is$ (1) $5$ (2) $10$ (3) $11$ (4) $13$