NEET Physics Work Energy and Power MCQs Set B

Question.  The heart of man pumps 5 litres of blood through the arteries per minute at a pressure of 150 mm of mercury. If the density of mercury be 13.6 ×10³ kg/m³ and g = 10m/s² then the power of heart in watt is :
(a) 1.70
(b) 1.50
(c) 3.0
(d) 2.35

Answer: A

Question.   A ball is thrown vertically downwards from a height of 20 m with an initial velocity v₀. It collides with the ground loses 50 percent of its energy in collision and rebounds to the same height. The initial velocity v₀ is :(Take g = 10 ms^–2)
(a) 20 ms^–1
(b) 10 ms^–1
(c) 28 ms^–1
(d) 14 ms^–1

Answer: A

Question.  A block of mass 10 kg, moving in x direction with a constant speed of 10 ms_–1, is subject to a retarding force F = 0.1 × J/m during its travel from x = 20 m to 30 m. Its final KE will be:
(a) 475 J
(b) 250 J
(c) 275 J
(d) 450 J

Answer: A

Question.  A particle of mass m moving in the x direction with speed 2v is hit by another particle of mass 2m moving in the y direction with speed v. If the collision is perfectly inelastic, the percentage loss in the energy during the collision is close to :
(a) 56%
(b) 62%
(c) 44%
(d) 50%

Answer: A

Question.  k is stretched by a small length x. It is further stretched by another small length y. The work done in the second stretching is
(a) 1/2 Ky(2x + y)
(b) 1/2 k (x + y)²
(c) 1/2 Ky²
(d) 1/2 K(x² + y²)

Answer: A

Question.  A particle of mass 10 g moves along a circle of radius 6.4 cm with a constant tangential acceleration. What is the magnitude of this acceleration if the kinetic energy of the particle becomes equal to 8 × 10^–4 J by the end of the second revolution after the beginning of the motion?
(a) 0.1 m/s²
(b) 0.18 m/s²
(c) 0.2 m/s²
(d) 0.15 m/s²

Answer: A

Question.  A person trying to lose weight by burning fat lifts a mass of 10 kg upto a height of 1 m 1000 times. Assume that the potential energy lost each time he lowers the mass is dissipated. How much fat will he use up considering the work done only when the weight is lifted up? Fat supplies 3.8 × 107 J of energy per kg which is converted to mechanical energy with a 20% efficiency rate. Take g = 9.8 ms^–2 :
(a) 12.89 × 10^–3 kg
(b) 2.45 × 10^–3 kg
(c) 9.89 × 10^–3 kg
(d) None of these

Answer: A

Question.  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/s².  The work done by the (i) gravitational force and the (ii) resistive force of air is
(a) (i) 10 J (ii) – 8.75 J
(b) (i) – 10 J (ii) –8.25 J
(c) (i) 100 J (ii) 8.75 J
(d) (i) 1.25 J (ii) –8.25 J

Answer: A

Question. Assertion : Graph between potential energy of a spring versus the extension or compression of the spring is a straight line.
Reason : Potential energy of a stretched or compressed spring, proportional to square of extension or compression
(a) If both the Assertion and Reason are incorrect
(b) If Assertion is correct but Reason is incorrect
(c) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion
(d) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion

Answer: A

Question. A time dependent force F = 6t acts on a particle of mass 1 kg. If the particle starts from rest, the work done by the force during the first 1 second will be
(a) 4.5 J
(b) 22 J
(c) 18 J
(d) 9 J

Answer: A

Question.   A particle of mass m moving in the x direction with speed 2v is hit by another particle of mass 2m moving in the y direction with speed v. If the collision is perfectly inelastic, the percentage loss in the energy during the collision is close to
(a) 56%
(b) 62%
(c) 44%
(d) 50%

Answer: A

Question.  A moving block having mass m, collides with another stationary block having mass 4m. The lighter block comes to rest after collision. When the initial velocity of the lighter block is v, then the value of coefficient of restitution (e) will be
(a) 0.25
(b) 0.4
(c) 0.8
(d) 0.5

Answer: A

Question. Assertion : A quick collision between two bodies is more violent than slow collision, even when initial and final velocities are identical.
Reason : The rate of change of momentum determines that the force is small or large.
(a) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion
(b) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion
(c) If Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect

Answer: A

Question.  The mass of a hydrogen molecule is 3.32×10^–27 kg. If 10²³ hydrogen molecules strike, per second, a fixed wall of area 2 cm² at an angle of 45° to the normal, and rebound elastically with a speed of 10³ m/s, then the pressure on the wall is nearly:
(a) 2.35 × 10³ N/m²
(b) 2.35 × 10² N/m²
(c) 2.35 × 10⁴ N/m²
(d) 2.35 × 10⁵ N/m²

Answer: A

Question.  A particle of mass m₁ moving with velocity v collides with a mass m₂ at rest, then they get embedded. Just after collision, velocity of the system
(a) decreases
(b) becomes zero
(c) increases
(d) remains constant

Answer: A

Question.  An electric pump is used to fill an overhead tank of capacity 9m³ kept at a height of 10m above the ground. If the pump takes 5 minutes to fill the tank by consuming 10 kW power the efficiency of the pump should be (g = 10 ms^–2)
(a) 30%
(b) 20 %
(c) 40 %
(d) 60 %

Answer: A

Question.  A force of 250 N is required to lift a 75 kg mass through a pulley system. In order to lift the mass through 3 m, the rope has to be pulled through 12m. The efficiency of system is
(a) 75%
(b) 33%
(c) 90%
(d) 50%

Answer: A