A car moving 20 km/h skids 30 m with locked brakes. how far will the car skid with locked breaks if it were traveling at 100 km/hr

Kinetic energy = (1/2) (mass) (speed) ²

Since the 'speed' in the KE formula is squared, if the car's speed

increases by 5 times, its kinetic energy increases by (5²) = 25 times.

The loss of kinetic energy in a skid is just the wo0rk done by friction

between the tires and pavement. So the skid distance is proportional

to the initial kinetic energy, and the car must skid 25 times as far when

it enters the skid at the higher speed.

25 x 30m = 750 meters