Worksheet: Mechanical Power

In this worksheet, we will practice calculating the power required for a force to do an amount of work on an object in an amount of time.

Q1:

A train engine does work at a rate of 5 0 0 0 W. How much time will this engine take to do 125 J of work?

Q2:

A rocket moves vertically upwards at a constant speed of 18 m/s. The weight of the rocket is 250 kN. What is the power supplied by the rocket’s engines? Give your answer in megawatts.

  • A 13.9 MW
  • B 45 MW
  • C 44.1 MW
  • D 4.5 MW
  • E 2.25 MW

Q3:

A horse pulls a cart for 50 seconds. The work done by the force applied by the horse during this time is 37 500 J. What is the power supplied by the horse?

Q4:

360 W of power is supplied to do 270 J of work. How much time is taken to do this amount of work?

Q5:

A power of 140 W is supplied to do work for a time of 2.5 seconds. How much work is done?

Q6:

Which of the following formulas correctly shows the relationship between the time taken to do an amount of work and the power supplied to do the work?

  • A 𝑃 = 𝑑 π‘Š
  • B 𝑃 = π‘Š 𝑑
  • C 𝑃 = π‘Š βˆ’ 𝑑
  • D 𝑃 = π‘Š 𝑑
  • E 𝑃 = π‘Š + 𝑑

Q7:

A construction worker has to push a heavy, loaded waste container to a disposal area. This task tires the worker out and he pauses several times to rest. The distance that the container is moved in each 10-second time interval is shown in the table. Whenever the worker pushes the container, an average force of 80 N is used to push it. What is the average power supplied by the worker over the ten time intervals?

Time Interval Number 1 2 3 4 5 6 7 8 9 10
Distance (m) 2.3 1.1 0 1.6 0.7 0 0 1.2 1.1 0.5

Q8:

The power supplied by a force over a 10-second time interval is shown in the graph.

How much work does the force do from 𝑑 = 0 s to 𝑑 = 2 s?

How much work does the force do from 𝑑 = 3 s to 𝑑 = 5 s?

How much work does the force do from 𝑑 = 2 s to 𝑑 = 3 s?

How much work does the force do from 𝑑 = 5 s to 𝑑 = 9 s?

Q9:

The work done by a force over a 10-second time interval is shown in the graph.

What instantaneous power does the force supply at 𝑑 = 3 s?

What instantaneous power does the force supply at 𝑑 = 6 s?

What average power does the force supply between 𝑑 = 7 s and 𝑑 = 9 s?

Q10:

Suppose that 260 J of work is done in 40 seconds. What power is required to do this amount of work?

Q11:

How much work is done in 600 seconds by the force from a car engine that has a power of 1 2 5 0 W?

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