00:04
We have a problem here that involves conservation of energy.
00:10
Couple of things to know here.
00:13
The coefficient of friction is equal to 0 .25.
00:22
So we're going to release the 100 -kilogram block.
00:26
This block is going to slide up 20 meters.
00:32
Over those 20 meters, what is the change in kinetic energy? that's what we're trying to find.
00:39
So i'm going to use conservation of energy, as i said.
00:45
So this mgh is going to change.
00:52
It's going to result in a change of kinetic energy and a change in thermal energy, which is the frictional force times the distance that it moves.
01:11
So that distance is going to be 20 meters.
01:13
That's what they told us.
01:16
So we need to know how much the height has changed.
01:20
We draw this triangle, 37 degrees, 20 meters.
01:28
That 37 degrees should let you know that's a 3, 4, or 5 triangle.
01:32
Or i can do trig...