physics
posted by jim .
This question is typical on some driver's license exams: A car moving at 50km/hr skids 15m with locked brakes.How far will the car skid with locked brakes at 120 km/h?

A cars kinetic energy is proportional to the square of it's speed. The energy dispensed in braking is proportional to the braking distance.
Therefore the braking distance is proportional to the square of the speed, as in (120 km/hr / 50 km/hr)² * 15m