Question

A 1000kg car is traveling along a level road at 20.00ms, when the brakes are applied long enough to do 50000 J of work.

1) what is the initial kinetic energy of the car?

2) if the car moved 100m while the brakes where applied, what was the average force exerted on the brakes.

Answer 1

In itial KE = (1/2)M V^2

Your 20.00 ms must be 20.00 m/s.

The brakes do not DO work; they absorb heat equal to the work done by the car (on the brakes) while slowing down.

Force x distance = Kinetic energy loss

Solve for the force.

Answer 2

Thank you.