WEBVTT

1
00:00:00.000 --> 00:00:08.928
Here is the problem: A 200 N force pulls a box 2.5 m at 30° to the direction of motion. How much work does it do?

2
00:00:09.378 --> 00:00:15.508
Use the work done by a constant force formula, rearranged for the unknown, in SI units.

3
00:00:16.308 --> 00:00:19.280
Formula: work done by a constant force.

4
00:00:19.730 --> 00:00:21.692
Substitute the known values.

5
00:00:22.492 --> 00:00:27.983
So the answer is work W equals 433.013 J.

6
00:00:28.434 --> 00:00:42.412
Only the component of the force along the displacement does work, hence the cos theta. Work is positive when the force has a component along the motion, negative when it opposes it (theta greater than 90°), and zero when it is perpendicular.

7
00:00:43.212 --> 00:00:48.854
Substituted every value back into the formula: both sides agree, which checks out.