00:01
All right, so we have a car skidding to a stop.
00:03
The mass of the car is 2 ,000 kilograms.
00:08
We're told the initial velocity before it starts to break is 25 meters per second.
00:16
And it takes a total distance of 60 meters before it comes to a stop.
00:23
And because it's stopping, we can say the final velocity is zero meters per second.
00:30
So what we can do here is in order to find the amount of energy that goes into the friction, or is dissipated through friction, we can just use the fact that the work, the work done by the friction is equal to the change in the kinetic energy.
00:52
So initially, we have a kinetic energy of one -half mv squared, where v is 25 meters per second.
01:02
And then at the end, there's no kinetic energy.
01:05
So that's, so k .e.
01:10
Final minus k .e.
01:14
Initial.
01:15
It's just going to be 0 minus 1ā2mv initial squared.
01:23
So then our work, oops, our work from the friction is negative, one -half, and we can actually ignore the negative sign.
01:36
We're just looking for the magnitude of the work done here, or the energy dissipated.
01:43
So one -half, so negative just means that work went in, or it's stopping it, so it went into stopping the car...