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.

Question

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.