WEBVTT

1
00:00:00.000 --> 00:00:05.968
Here is the problem: A motor does 5000 J of work in 20 s. What is its power?

2
00:00:06.418 --> 00:00:10.574
Use the power formula, rearranged for the unknown, in SI units.

3
00:00:11.374 --> 00:00:12.802
Formula: power.

4
00:00:13.252 --> 00:00:15.156
Substitute the known values.

5
00:00:15.956 --> 00:00:19.961
So the answer is power P equals 250 W.

6
00:00:20.411 --> 00:00:27.691
Power is the rate of doing work: one watt is one joule per second. The same work done in half the time needs twice the power.

7
00:00:28.490 --> 00:00:34.167
Substituted every value back into the formula: both sides agree, which checks out.