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

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.

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

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?

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?