JEE Physics Work Energy and Power MCQs Set 03

Question. A body of mass 1 kg is thrown upwards with a velocity 20 m/s. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? (g = 10 m/s²)
(a) 20 J
(b) 10 J
(c) 30 J
(d) 40 J

Answer: A

Question. Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional forces are 10% of energy. How much power is generated by the turbine? (g = 10 m/s2)
(a) 8.1 kW
(b) 7.0 kW
(c) 10.2 kW
(d) 12.3 kW

Answer: A

Question. 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
(a) 1 : 2
(b) 1 : 3
(c) 2 : 1
(d) 3 : 1

Answer: A

Question. A car of mass m starts from rest and accelerates so that the instantaneous power delivered to the car has a constant magnitude P₀. The instantaneous velocity of this car is proportional to
(a) t^1/2
(b) t^1/3
(c) t^1/4
(d) None of this

Answer: A

Question. A body projected vertically from the earth reaches a height equal to earth's radius before returning to the earth. The power exerted by the gravitational force is greatest
(a) At the instant just before the body hits the earth
(b) It remains constant all through
(c) At the highest position of the body
(d) At the instant just after the body is projected

Answer: A

Question. If a force of 9 N is acting on a body, then find instantaneous power supplied to the body when its velocity is 5 m/s in the direction of force
(a) 45 watt
(b) 195 watt
(c) 75 watt
(d) 100 watt

Answer: A

Question. An engine pumps water through a hose pipe. Water passes through the pipe and leaves it with a velocity of 2 m/s. The mass per unit length of water in the pipe is 100 kg/m. What is the power of the engine?
(a) 800 W
(b) 400 W
(c) 200 W
(d) 100 W

Answer: A

Question. The coefficient of restitution, e, for a perfectly elastic collision is
(a) 1
(b) –1
(c) 0
(d) None o this

Answer: A

Question. A particle of mass m₁ moves with velocity v₁ and collides with another particle at rest of equal mass. The velocity of the second particle after the elastic collision is
(a) v₁
(b) 2v₁
(c) –v₁
(d) None of this

Answer: A

Question. Two identical balls A and B collide head-on elastically. If velocities of A and B, before the collision, are + 0.5 m/s and - 0.3 m/s respectively then their velocities, after the collision, are respectively
(a) – 0.3 m/s and + 0.5 m/s
(b) + 0.5 m/s and + 0.3 m/s
(c) – 0.5 m/s and + 0.3 m/s
(d) + 0.3 m/s and – 0.5 m/s

Answer: A

Question. A moving body of mass m and velocity 3 km/h collides with a rest body of mass 2m and sticks to it. Now the combined mass starts to move. What will be the combined velocity?
(a) 1 km/h
(b) 2 km/h
(c) 4 km/h
(d) 3 km/h

Answer: A

Question. A body of mass 1 kg is thrown upwards with a velocity 20 m/s. It momentarily comes to rest after attaining a height of 18 m. How much energy is lost due to air friction? (g = 10 m/s²)
(a) 20 J
(b) 10 J
(c) 30 J
(d) 40 J

Answer: A

Question. Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional forces are 10% of energy. How much power is generated by the turbine? (g = 10 m/s²)
(a) 8.1 kW
(b) 7.0 kW
(c) 10.2 kW
(d) 12.3 kW

Answer: A

Question. 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
(a) 1 : 2
(b) 1 : 3
(c) 2 : 1
(d) 3 : 1

Answer: A

Question. A car of mass m starts from rest and accelerates so that the instantaneous power delivered to the car has a constant magnitude P₀. The instantaneous velocity of this car is proportional to
(a) t^1/2
(b) t^1/3
(c) t^1/4
(d) None of this

Answer: A

Question. A body projected vertically from the earth reaches a height equal to earth's radius before returning to the earth. The power exerted by the gravitational force is greatest
(a) At the instant just before the body hits the earth
(b) It remains constant all through
(c) At the highest position of the body
(d) At the instant just after the body is projected

Answer: A

Question. If a force of 9 N is acting on a body, then find instantaneous power supplied to the body when its velocity is 5 m/s in the direction of force
(a) 45 watt
(b) 195 watt
(c) 75 watt
(d) 100 watt

Answer: A

Question. An engine pumps water through a hose pipe. Water passes through the pipe and leaves it with a velocity of 2 m/s. The mass per unit length of water in the pipe is 100 kg/m. What is the power of the engine?
(a) 800 W
(b) 400 W
(c) 200 W
(d) 100 W

Answer: A

Question. The coefficient of restitution, e, for a perfectly elastic collision is
(a) 1
(b) –1
(c) 0
(d) None o this

Answer: A

Question. A particle of mass m₁ moves with velocity v₁ and collides with another particle at rest of equal mass. The velocity of the second particle after the elastic collision is
(a) v₁
(b) 2v₁
(c) –v₁
(d) None of this

Answer: A

Question. Two identical balls A and B collide head-on elastically. If velocities of A and B, before the collision, are + 0.5 m/s and - 0.3 m/s respectively then their velocities, after the collision, are respectively
(a) – 0.3 m/s and + 0.5 m/s
(b) + 0.5 m/s and + 0.3 m/s
(c) – 0.5 m/s and + 0.3 m/s
(d) + 0.3 m/s and – 0.5 m/s

Answer: A

Question. A moving body of mass m and velocity 3 km/h collides with a rest body of mass 2m and sticks to it. Now the combined mass starts to move. What will be the combined velocity?
(a) 1 km/h
(b) 2 km/h
(c) 4 km/h
(d) 3 km/h

Answer: A