CK-12-Physics-Concepts - Intermediate

http://www.ck12.org Chapter 8. Work, Power, and Simple Machines

8.2 Power

• Define power.


• Given two of the three variables inP=Wt, calculate the third.

Typical Pressurized Water Reactors (PWR), a type of nuclear power reactor originally built in the 1970s, produce
1100 to 1500 megawatts, or about 1,500,000,000 Joules/second. By comparison, a windmill farm with hundreds of
individual windmills produces about 5 megawatts (5,000,000 Joules/second).

Power

Poweris defined as the rate at which work is done, or the rate at which energy is transformed.

Power=

Work

Time

In SI units, power is measured in Joules per second, which is given a special name: the watt,W.

1.00 watt = 1.00 J/s

Another unit for power that is fairly common is horsepower.

1.00 horsepower = 746 watts

Example Problem: A 70.0 kg man runs up a long flight of stairs in 4.0 s. The vertical height of the stairs is 4.5 m.
Calculate the power output of the man in watts and horsepower.