This question is typical on some driver's license exams: A car moving at 50 km/hkm/h skids 15 mm with locked brakes. How far will the car skid with locked brakes at 110 km/hkm/h ?

Question

This question is typical on some driver's license exams: A car moving at 50 km/hkm/h skids 15 mm with locked brakes. How far will the car skid with locked brakes at 110 km/hkm/h ?

Answer 1

During skidding the kinetic energy of the car is dissipated by the

work of the force of friction, so the two are equal.

Kinetic energy is proportional to the square of velocity, while

work is linear in the distance over which the force is applied.

Therefore the skidding distance, s, is proportional to the square of speed.

Substituting actual numbers:

s = 15 mm x (110/50)² = 72.6 mm