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Free Work and Energy MCQs with Answers

748 Work and Energy MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Work transfers energy when a force causes displacement, while kinetic energy, gravitational potential energy and power describe motion, position and the rate of energy transfer. The work-energy theorem links net work with change in kinetic energy, and efficiency accounts for energy losses rather than treating them as energy destruction.

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WorkKinetic EnergyPotential EnergyPowerWork-Energy TheoremEnergy Losses and Efficiency
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748 questions · page 24 of 38

461. A man of mass 50 kg jumps to a height of 1 m. His potential energy at the highest point is (g = 10 m/s2):

  • A. 50 J
  • B. 60 J
  • C. 500J
  • D. 600 J

Explanation: Potential energy = mgh = 50 x 10 x 1 = 500J

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Correct answer: 500J

462. In 10 seconds, the elevator picks a weight of 1000 N over a distance of 10 m at a constant velocity. Its power is:

  • A. 10 Watt
  • B. 100 Watt
  • C. 1000 Watt
  • D. 10,000 Watt

Explanation: Power = work done / time Work done = Force x displacement = 1000 x 10 = 10000J Power = 10000 / 10 = 1000 W OR Power = mgh/t W = mg = 1000…

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Correct answer: 1000 Watt

463. An object of 5 kg is pulled horizontally by a force of 50 N through a displacement of 10m. The work done by gravity is:

  • A. 250 J
  • B. 500 J
  • C. Zero
  • D. 5 kJ

Explanation: Since we are required to find the work done by gravity. So, W = Fdcos90o = 0 J

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Correct answer: Zero

464. The average power and instantaneous power become equal if work is done at:

  • A. Any rate
  • B. Uniform rate
  • C. Variable rate
  • D. High rate

Explanation: The average power and instantaneous power become equal if work is done at a constant rate.

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Correct answer: Uniform rate

465. The power is one kilowatt if work is done at the rate of:

  • A. 1000 Js-1
  • B. 1000 J min-1
  • C. 100 Js-1
  • D. 1000 Jh-1

Explanation: Work done by a body in one second is known as power. P = 1kW = 1000 W 1000 Js-I = 1000 J work in one second

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Correct answer: 1000 Js-1

466. Kilowatt hour is the unit of:

  • A. Power
  • B. Force
  • C. Momentum
  • D. Energy

Explanation: One kilowatt hour is the work done (energy) in One hour by an agency whose power is one kilowatt.

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Correct answer: Energy

467. Which is the biggest unit of energy:

  • A. erg
  • B. joule
  • C. watt hour
  • D. kilowatt hour

Explanation: 1KWh=3.6 x 10^6J 1erg = 10-7J 1Wh = 3.6 x 10^3J 1kWh> 1Wh > 1J > 1erg

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Correct answer: kilowatt hour

468. A 2 kg block is thrown upward from a point 20m above Earth's surface. At what height above Earth's surface will the gravitational potential energy of the Earth-block system have increased by 500 J? (g = 10 m/s2)

  • A. 5m
  • B. 45m
  • C. 25m
  • D. 70m

Explanation: Gravitational potential energy is given by P.E = mgh 500 = (2)(10)h → h = 500 / 20 = 25 m

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Correct answer: 25m

469. The amount of work done is pumping water out of a cubicle vessel of height 1 m is: (g= 10 m/s2)

  • A. 1000 J
  • B. 5000 J
  • C. 10,000 J
  • D. 100 J

Explanation: ρ = m/V → m=ρV = (1000)(1x1x1) = 1000 kg W = P.E. = mgh = (1000)(10)(1) = 10000 J

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Correct answer: 10,000 J

470. A crane can raise a body of mass 100 kg vertically upward with a speed of 5 m/s. The power of its engine is (g= 10 m/s2):

  • A. 2 kW
  • B. 10 kW
  • C. 5 kW
  • D. 4 kW

Explanation: P = Fv = mgv = (100)(10)(5) = 5000 watt = 5 kW

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Correct answer: 5 kW

471. A 50 kg body is accelerated from rest to 20 m/s in 10s. What is the amount of work done?

  • A. 1000 J
  • B. 2000 J
  • C. 10,000 J
  • D. 20,000 J

Explanation: Work done = 1/2 mvf2--- mvi2 = 1/2(50) (202- 02) = 25(400) 10000 J

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Correct answer: 10,000 J

472. A ball, starting at point X, rolls down the hill shown in the diagram. At which point does the ball have half of its maximum kinetic energy? (Ignore friction)

  • A. A
  • B. B
  • C. C
  • D. D

Explanation: Gain in kinetic energy = loss in gravitational potential energy. The ball will have maximum kinetic energy at the bottom of the hill.

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Correct answer: C

473. During rainfall, a certain drop of radius "r" falls through a height "h" above the ground. The work done by the gravitational force is proportional to the:

  • A. r3
  • B. r2
  • C. r
  • D. r4

Explanation: Work done by gravitational force. W = mgh

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Correct answer: r3

474. A 5 kg block is moved from the rest through a distance of 4 m along the x-direction. A force equal to 20 N acts on it. If the block acquires a K.E. equal to 40 J, what is the angle the force makes with x-axis?

  • A. 0o
  • B. 30o
  • C. 45o
  • D. 60o

Explanation: By work energy principle Work = K.E Fdcosθ = K.E cosθ = K.E/Fd = 40/(20)(4) = 1/2 θ = cos-1(1/2) = 60o

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Correct answer: 60o

475. A bullet of mass "m" is fired from horizontally with a velocity "v" on to a wooden block of mass "m" and gets embedded in it. The kinetic energy of the bullet + block system is:

  • A. Option A
  • B. Option B
  • C. Option C
  • D. Option D

Explanation: By law of conservation of linear momentum Total initial momentum = Total final momentum mv = mv' + Mv' mv = (m+ M)v' v' = mv/ M+m

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Correct answer: Option D

476. A force F acting on an object varies with distance x as shown in fig. The work done by the force in moving the object from x = 0 to x = 6 m is:

  • A. 18 J
  • B. 13.5 J
  • C. 9 J
  • D. 4.5 J

Explanation: W = Area under F - x graph W= 1/2 (Sum of parallel sides) (Perpendicular distance between parallel sides) = 1/2(6+3)(3) =13.5 J

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Correct answer: 13.5 J

477. If force and displacement of particle in direction of force are doubled. Work would be:

  • A. Double
  • B. Half
  • C. 1/4 times
  • D. 4 times

Explanation: Work = Force × Displacement If force and displacement both are doubled then work would be four times.

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Correct answer: 4 times

478. The diagram shows a flight of stairs. How much useful work is done by a person weighing 600 N when climbing the stairs?

  • A. 120 J
  • B. 1800 J
  • C. 2400 J
  • D. 3000 J

Explanation: By conservation of energy, Useful work done = gain in gravitational potential energy = mgh = (600 N) (3 m)= 1800 J

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Correct answer: 1800 J

479. A tennis ball is dropped on to a horizontal surface. As the ball bounces up and down, the height of each bounce gradually decreases. During the motion:

  • A. the kinetic energy of the ball is constant
  • B. the potential energy of the ball is constant
  • C. the sum of the kinetic and potential energies of the ball is constant
  • D. the total energy of the ball, ground and air is constant

Explanation: The principle of conservation of energy states that the total energy of a system remains constant.

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Correct answer: the total energy of the ball, ground and air is constant

480. What will be the ratio of kinetic energies of alpha particle and proton if their linear momentum will be same?

  • A. 18 : 1
  • B. 1: 4
  • C. 4 : 1
  • D. 104 : 1

Explanation: Mass of α-particle=6.644x 10-27kgmass of proton = 1.672 x 10-27 kgPα =Pp

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Correct answer: 1: 4
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