Interactive exercise. Assistance may be required. There are three basic formulas you can use to calculate power. Scroll over the empty cells to read more.

The metric unit of power is the watt (w).

1 watt = 1 Joule/second
(Remember: 1 Joule = 1 Newton x meter)

The watt is a small unit, so you will often see power ratings in kilowatts.

1 kilowatt = 1,000 watts

You might see power rating for motors in horsepower (hp).

1 horsepower = 746 watts

Solve It

Interactive exercise. Assistance may be required. You are not often given information in the same order as the formula. Take a few moments to see if you can figure out how to solve the problems below. Mouse over the empty cells to check your answers.

Scenario 1:

A machine runs at 100 hp and has been running for 60 seconds. How much work has been done?

Scenario 2:

A 60 Watt light bulb is turned on at 1:00 p.m. and is turned off at 1:15 p.m. How much energy did the light bulb expend during the time it was on?

Scenario 3:

A softball launcher runs at 1 hp and shoots at a velocity of 5 m/s. What is the force of each ball as it is launched?