00:01
So in this question we're thinking about a 28 kilogram child playing on a swing, who is pulled back by an angle of phi, which is 43 .0 degrees, on ropes that are l equals 1 .90 metres long.
00:23
So what's the potential energy for the child just before she's released? u, the potential energy, is m, g, h.
00:32
So that's m g times the sign of phi.
00:45
Sorry, that's not right, it's 1 minus the cos of phi.
00:54
So we can work that out with a calculator.
00:56
We've got 28 times g, which is 9 .81 meters per second squared, times 1 minus the cosine of 43 degrees.
01:06
And that gives us 73 .79 joules.
01:14
So then how fast will she be moving? so that's part a.
01:18
Part b is how fast is she moving at the bottom of the swing? well, we're going to convert this potential energy into kinetic energy...