# 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 5,000 W. How much time will this engine take to do 125 J of work?

Q2:

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

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
• B
• C
• D
• E

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 Distance (m) 1 2 3 4 5 6 7 8 9 10 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 = 0 s to = 2 s?

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

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

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

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

What average power does the force supply between = 7 s and = 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 1,250 W?

Q12:

The graphs (a), (b), (c), (d), and (e) show the change with time of forces acting on a car that travels at a constant speed while increasing the power from its engine. The force from the engine is shown in blue and the force that resists the carβs motion is shown in red. Which graph correctly shows the changes of the forces with time?

• A(c)
• B(e)
• C(a)
• D(b)
• E(d)