MDCAT Physics chapter 3: Physics · Work, power and energy MCQs with answers

By Team Megalecture · Updated 4 Nov 2026

18 exam-style questions on Physics · Work, power and energy, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.

18 questions · 2 topics · 10 per test

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What chapter 3 covers

Ten Physics · Work, power and energy questions with answers

Try each one, then open the answer. These ten stay the same; the test draws new ones every time.

1. The momentum of a body is increased by 50%. Its kinetic energy increases by

  1. A
    50%
  2. B
    100%
  3. C
    125%
  4. D
    225%
Show answer

Answer: C. K = p2/2m, so K becomes (1.5)2 = 2.25 times its old value, an increase of 125%. 225% is the new kinetic energy as a percentage of the old one, not the increase.

2. A block slides down a rough inclined plane at constant velocity. Which statement is correct?

  1. A
    its kinetic energy increases as its potential energy decreases
  2. B
    its total mechanical energy stays the same throughout
  3. C
    the potential energy it loses equals the work done against friction
  4. D
    gravity does no work on it because its speed is constant
Show answer

Answer: C. Its speed, and so its kinetic energy, stays constant while it loses height. Gravity does positive work mgh and friction does an equal amount of negative work, so the lost potential energy is all used against friction (it appears as heat).

3. The force on a body rises uniformly from 0 to 20 N as it moves the first 2.0 m, and then stays at 20 N for the next 3.0 m. The total work done by the force is

  1. A
    100 J
  2. B
    60 J
  3. C
    50 J
  4. D
    80 J
Show answer

Answer: D. Work = area under the force–displacement graph: triangle ½ × 2.0 × 20 = 20 J plus rectangle 3.0 × 20 = 60 J, a total of 80 J. 100 J takes the force as 20 N all the way.

4. An electric motor takes 2.0 kW of electrical power and lifts a 100 kg load vertically at a steady 1.5 m s−1. Taking g = 10 m s−2, the efficiency of the motor is

  1. A
    50%
  2. B
    7.5%
  3. C
    67%
  4. D
    75%
Show answer

Answer: D. Useful output power = Fv = mgv = 100 × 10 × 1.5 = 1500 W, so efficiency = 1500/2000 × 100% = 75%. 7.5% leaves out g.

5. A body of mass m has linear momentum of magnitude p. Its kinetic energy is

  1. A
    p2/m
  2. B
    mp2/2
  3. C
    2m/p2
  4. D
    p2/2m
Show answer

Answer: D. Put v = p/m into K = ½mv2: K = ½m(p/m)2 = p2/2m. So for equal momentum the lighter body has the greater kinetic energy.

6. A 50 kg girl runs up a staircase of 40 steps, each 15 cm high, in 10 s. Taking g = 10 m s−2, her average power against gravity is

  1. A
    3000 W
  2. B
    30 W
  3. C
    7.5 W
  4. D
    300 W
Show answer

Answer: D. Height climbed = 40 × 0.15 = 6.0 m, so the work is mgh = 50 × 10 × 6.0 = 3000 J and the power is 3000/10 = 300 W. 3000 W forgets to divide by the time, and 7.5 W counts only one step.

7. A ball is thrown vertically downwards at 10 m s−1 from a height of 15 m. Taking g = 10 m s−2 and ignoring air resistance, its speed just before it hits the ground is

  1. A
    17 m s−1
  2. B
    27 m s−1
  3. C
    20 m s−1
  4. D
    14 m s−1
Show answer

Answer: C. Energy conservation: ½v2 = ½u2 + gh, so v2 = 100 + 2 × 10 × 15 = 400 and v = 20 m s−1. 17 m s−1 ignores the initial speed, and 27 m s−1 adds speeds instead of energies.

8. A 1.0 kg book lies on a shelf 2.0 m above the floor. Taking g = 10 m s−2, its gravitational potential energy measured from the top of a table 0.80 m high is

  1. A
    20 J
  2. B
    12 J
  3. C
    8.0 J
  4. D
    28 J
Show answer

Answer: B. Potential energy is measured from the chosen reference level: h = 2.0 − 0.80 = 1.2 m, so mgh = 1.0 × 10 × 1.2 = 12 J. 20 J measures from the floor, and 8.0 J uses the height of the table itself.

9. A 2.0 kg box is pushed at a steady speed for 5.0 m up a smooth slope inclined at 30° to the horizontal. Taking g = 9.8 m s−2, the work done against gravity is

  1. A
    98 J
  2. B
    49 J
  3. C
    85 J
  4. D
    10 J
Show answer

Answer: B. Work against gravity = mgh, where h = 5.0 sin 30° = 2.5 m: 2.0 × 9.8 × 2.5 = 49 J. 98 J multiplies the weight by the distance along the slope instead of the height gained.

10. One horsepower (hp) is equal to

  1. A
    1000 W
  2. B
    746 W
  3. C
    100 W
  4. D
    550 W
Show answer

Answer: B. 1 hp = 746 W; it is a unit of power still used to rate motors and engines. 550 is the number of foot-pounds per second in 1 hp, not the number of watts.

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Physics · Work, power and energy: questions students ask

How many Physics · Work, power and energy MCQs are there?

18, each with the answer and a short explanation, across 2 topics: Work and power, Energy and its conservation. Every chapter test draws ten of them, so you can take it many times.

Is the MDCAT Physics chapter 3 test free?

Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.

How is the chapter test marked?

The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.

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