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Work and Energy MCQs — Physics (page 2)

60 multiple-choice questions on Work and Energy from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

26. Which of these is a non-conservative force?

  1. gravitational force
  2. elastic (spring) force
  3. electrostatic force
  4. friction

Answer: D) friction

Explanation: Work done against friction depends on the path length. SLO P-11-B-31 · Understanding

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27. With u = 0, the equation v^2 = 2ad gives d =

  1. v2a
  2. 2av^2
  3. 2av^2
  4. v^22a

Answer: D) v^22a

Explanation: Rearranging. SLO P-11-B-29 · Application

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28. If the mass is doubled at the same speed, the kinetic energy:

  1. quadruples
  2. is unchanged
  3. halves
  4. doubles

Answer: D) doubles

Explanation: K propto m. SLO P-11-B-29 · Application

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29. A 0.05 kg body moves at 400 m/s. Its kinetic energy is:

  1. 10 J
  2. 4000 J
  3. 2000 J
  4. 8000 J

Answer: B) 4000 J

Explanation: K = 12mv^2 = 12(0.05)(400)^2 = 4000 J. SLO P-11-B-29 · Application

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30. Area below the displacement axis on a force–displacement graph represents:

  1. positive work
  2. no work
  3. power
  4. negative work (force opposite to displacement)

Answer: D) negative work (force opposite to displacement)

Explanation: e.g. work done by friction. SLO P-11-B-30 · Application

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31. Work done against friction is mainly converted into:

  1. gravitational potential energy
  2. heat (internal energy)
  3. elastic potential energy
  4. mass

Answer: B) heat (internal energy)

Explanation: It cannot be recovered as mechanical energy. SLO P-11-B-31 · Understanding

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32. A conservative force is one for which the work done:

  1. depends on the path
  2. is independent of the path taken between two points
  3. is always zero
  4. is always negative

Answer: B) is independent of the path taken between two points

Explanation: e.g. gravity. SLO P-11-B-31 · Understanding

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33. A 2 kg body moving at 5 m/s is brought to rest by a constant resistive force in 10 m. The resistive force is:

  1. 1 N
  2. 1.25 N
  3. 2.5 N
  4. 5 N

Answer: C) 2.5 N

Explanation: Work done by friction = loss in KE: fd = 12mu^2 Rightarrow f = 2.5 N. SLO P-11-B-32 · Application

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34. A 5 kg body falls 20 m from rest against a constant air resistance of 9 N. Its speed on reaching the ground is (g = 9.8):

  1. 8.94 m/s
  2. 35.8 m/s
  3. 17.9 m/s
  4. 19.8 m/s

Answer: C) 17.9 m/s

Explanation: mgh - fh = 12mv^2 Rightarrow 980 - 180 = 800 J; v = 17.9 m/s. SLO P-11-B-32 · Application

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35. A box is pushed 5 m along a floor and back again to its start. The work done against friction is:

  1. not zero — it is twice the one-way work
  2. negative
  3. zero
  4. equal to the change in PE

Answer: A) not zero — it is twice the one-way work

Explanation: Friction opposes motion in both directions. SLO P-11-B-31 · Understanding

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36. A 0.145 kg body moves at 40 m/s. Its kinetic energy is:

  1. 2.9 J
  2. 116 J
  3. 58 J
  4. 232 J

Answer: B) 116 J

Explanation: K = 12mv^2 = 12(0.145)(40)^2 = 116 J. SLO P-11-B-29 · Application

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37. Each small square on a force–displacement graph represents 2 N × 0.5 m. 40 squares lie under the curve. The work done is:

  1. 20 J
  2. 80 J
  3. 100 J
  4. 40 J

Answer: D) 40 J

Explanation: Each square = 1 J, so 40 J. SLO P-11-B-30 · Application

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38. A 60 kg body falls from rest through 5 m and reaches 8 m/s. The work done against air resistance is (g = 9.8):

  1. 2940 J
  2. 510 J
  3. 2040 J
  4. 1020 J

Answer: D) 1020 J

Explanation: Loss of PE = mgh = 2940 J; gain of KE = 1920 J; work against friction = 1020 J. SLO P-11-B-32 · Application

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39. A 2 kg book is lifted 1 m by one route and 1 m by a longer zig-zag route. The work done against gravity is:

  1. the same both ways (19.6 J)
  2. zero for both
  3. smaller for the zig-zag route
  4. larger for the zig-zag route

Answer: A) the same both ways (19.6 J)

Explanation: Gravity is conservative: mgh = 2 9.8 1. SLO P-11-B-31 · Understanding

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40. The work–energy theorem states that the net work done on a body equals:

  1. the change in its kinetic energy
  2. its momentum
  3. its potential energy
  4. the force on it

Answer: A) the change in its kinetic energy

Explanation: Wnet = Delta K. SLO P-11-B-32 · Application

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41. A 1000 kg body moves at 20 m/s. Its kinetic energy is:

  1. 2 10^5 J
  2. 4 10^5 J
  3. 1 10^5 J
  4. 10,000 J

Answer: A) 2 10^5 J

Explanation: K = 12mv^2 = 12(1000)(20)^2 = 2 10^5 J. SLO P-11-B-29 · Application

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42. A 0.5 kg ball thrown up at 20 m/s rises only 18 m because of air resistance (g = 9.8). The energy lost to air is:

  1. 100 J
  2. 11.8 J
  3. 0 J
  4. 88.2 J

Answer: B) 11.8 J

Explanation: K0 = 100 J; mgh = 0.5 9.8 18 = 88.2 J; lost = 11.8 J. SLO P-11-B-32 · Application

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43. A potential energy can be defined only for:

  1. conservative forces
  2. non-conservative forces
  3. all forces
  4. friction

Answer: A) conservative forces

Explanation: Path-independence allows a unique potential energy. SLO P-11-B-31 · Understanding

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44. Electrostatic force between charges is:

  1. conservative
  2. path-dependent
  3. frictional
  4. non-conservative

Answer: A) conservative

Explanation: It has an electric potential energy. SLO P-11-B-31 · Understanding

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45. A force of 20 N accelerates a 4 kg body from rest over 10 m (no friction). Its final kinetic energy is:

  1. 200 J
  2. 80 J
  3. 50 J
  4. 800 J

Answer: A) 200 J

Explanation: Work done = Fd = 200 J = gain in KE. SLO P-11-B-29 · Application

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46. A body has momentum 10 kg m/s and mass 2 kg. Its kinetic energy is:

  1. 10 J
  2. 100 J
  3. 50 J
  4. 25 J

Answer: D) 25 J

Explanation: K = p^22m = 1004 = 25 J. SLO P-11-B-29 · Application

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47. A ball dropped in a viscous liquid reaches terminal velocity. Afterwards, the loss of PE goes into:

  1. work against viscous drag (heat)
  2. gain of KE
  3. nothing
  4. elastic energy

Answer: A) work against viscous drag (heat)

Explanation: KE is constant at terminal velocity. SLO P-11-B-32 · Application

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48. The work done by a conservative force around any closed path is:

  1. always negative
  2. maximum
  3. equal to the path length
  4. zero

Answer: D) zero

Explanation: You return to the same potential energy. SLO P-11-B-31 · Understanding

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49. Kinetic energy and momentum are related by:

  1. K = pm
  2. K = p2m
  3. K = 2mp^2
  4. K = p^22m

Answer: D) K = p^22m

Explanation: p = mv Rightarrow p^22m = 12mv^2. SLO P-11-B-29 · Application

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50. To derive K = 12mv^2, a force F accelerates a mass from rest through distance d. Which equation of motion is used?

  1. v = u + at
  2. F = Delta pDelta t
  3. v^2 = u^2 + 2ad
  4. d = vt

Answer: C) v^2 = u^2 + 2ad

Explanation: It links speed and distance without time. SLO P-11-B-29 · Application

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