A ball rolls into the street ahead of you, and you must stop. Which distances make up your total stopping distance?

Correct answer: Perception, reaction and braking distance, from when you see the ball

Why

Perception and reaction together take an average driver about 1.5 to 2 seconds, and the car covers that distance before it starts to slow. Speed has the largest effect: the manual says that stopping distance grows about four times when speed doubles, and at 50 mph on dry pavement with good brakes the braking part alone is about 158 feet. This is why a low speed near children, parked cars and crosswalks matters so much.

Verified against New Hampshire Driver's Manual · Stopping distance · p. 22