00:01
Okay, we have a watermelon dropped from this building, 18 .5 meters tall, just called height h.
00:09
It's a 4 .5 kilogram water melon.
00:11
We want to find the work done by gravity.
00:14
So, remember that work is a force times distance.
00:24
And if the force and the distance, where the movement of the object, are in the same direction, positive work.
00:32
So you could also write this as a dot product, if you know what that is.
00:39
Basically, if the force is in the same direction as the displacement, positive work.
00:44
So we have a watermelon.
00:47
What force is acting on it? gravity.
00:51
M .g.
00:52
Because that's the, we're trying to find the work done by gravity.
00:55
What's the displacement that it is displaced through? it's that distance h.
01:02
And it's being displaced down.
01:04
So we'll call it d, i guess.
01:07
That's the direction of the displacement.
01:08
So the work is equal to the force, mg, times the displacement h.
01:15
It's worked in my gravity.
01:18
And it's positive because the force is acting in the same direction as the watermelon's moving.
01:25
So mgh.
01:28
So 4 .5 kilogram watermelon, 18 .5 meters tall.
01:33
This is 8116 .683.
01:38
6 .8 .3 joules.
01:46
Okay...