How does the braking distance at 40 mph compare to that at 20 mph?

The correct understanding of how braking distance changes with speed reveals that as speed increases, the braking distance increases at a quadratic rate, mainly due to the physics involved in stopping a vehicle.

When a vehicle is traveling at a certain speed, the kinetic energy which must be dissipated to stop it also increases with the square of the speed. Specifically, stopping distance is related to the square of the speed, which means if the speed doubles, the braking distance increases fourfold.

In this case, when comparing the braking distance at 20 mph and 40 mph, the distance required to come to a complete stop at 40 mph is four times greater than that at 20 mph due to this relationship. Understanding this principle is crucial for safe driving and effective braking in emergency situations, as it emphasizes the importance of maintaining a safe speed and distance from other vehicles on the road.