00:01
All right, so let's say we have a car traveling along the road, and the mass of the car is, let's see, 2 ,000 kilograms, and it's got a speed of 25 meters per second, and it stops, it skids to a stop in a distance of 60 meters.
00:20
So we want to find the energy dissipation due to friction, first off, and so this is easy.
00:25
The work done by friction is just going to be equal to the change in kinetic energy of the car.
00:29
And so the change in kinetic energy is just minus one -half in v squared.
00:33
So this is minus one -half of 2 ,000, which is negative 1 ,000 kilograms times 25 squared.
00:42
So that's 625 meters squared per second squared.
00:46
And so we can write this as negative 6 .25 times 10 to the 5th joules.
00:54
And then for part b, we want to find the coefficient of friction between the tires and the surface of the road.
00:59
So the acceleration of the car is going to equal v squared over 2x in magnitude...