Question

A 750 kg car moving at 25 m/s has Kinetic Energy. To stop the car requires work. On snowy roads, the force of friction that can

stop a car reduces to only about 725 N.
a. How much work must be done to stop the car? (Hint: What is the car's kinetic energy?)
b. How far will the car travel before stopping if the only force stopping it is friction between the tires and the road?

Answer 1

a. By the work-energy theorem, the total work required to stop the car is equal to the change in its kinetic energy,

W = 0 - 1/2 (750 kg) (25 m/s)² ≈ -230 kJ

b. The car covers a distance x as it stops such that

W = (-725 N) x ==> x ≈ 320 m