Explain why a car travelling at a higher speed takes a longer distance to stop when the driver applies the brakes, compared with the same car travelling at a lower speed.

1. The driver’s reaction time causes a thinking distance, which is the distance the car travels before the brakes are applied.
2. At a higher speed the car covers a greater distance during that same reaction time, so the thinking distance is larger.
3. The car’s kinetic energy is ½mv²; a higher speed gives a larger kinetic energy.
4. The braking force must perform more work to remove this extra kinetic energy, so the braking distance is longer.
5. The total stopping distance, the sum of thinking distance and braking distance, is therefore greater when the car is travelling faster.