00:01
7 .69.
00:02
So we have an elevator whose cable breaks when it's 22 and a half meters above the top of a gigantic spring that's in the elevator shaft for some reason.
00:16
So first we want to find the work that gravity does between the point where the cable breaks and when the elevator comes into contact with the spring.
00:31
And then we want to find the speed of the elevator just before it hits the spring, and then we want to find the amount that the spring will compress.
00:39
And here, work is being done both by the spring and by gravity, so we'll have to be a little bit careful.
00:49
So to begin with, the only force acting on the elevator while it's falling until it hits the spring is gravity.
01:00
So the total work that does is going to be the weight of the car, times the distance it falls.
01:09
There's a 22 .5 meters here.
01:12
And then the cosine of the angle between the force and the displacement is one because the angle is zero.
01:26
So this is 2 .04 times 10 to the 5th joules.
01:41
Because gravity is the only force doing any work on the car until it hits the spring.
01:53
The work done by gravity is equal to the change in kinetic energy...