What is the stopping distance?

The stopping distance refers specifically to the distance from when the brakes engage until the vehicle comes to a complete stop. This measures the effectiveness of the braking system and accounts for the time it takes for the brakes to exert force on the wheels, reducing the speed of the vehicle.

When considering this definition, it is essential to acknowledge that the stopping distance is influenced by various factors such as the vehicle's speed, road conditions, and the efficiency of the braking system.

The first option describes the general reaction time and hazard perception but does not specifically capture the braking part of stopping. The third option focuses on total distance traveled while speeding, which is unrelated to stopping distance as it doesn't involve the braking process. The fourth option about emergency braking does not encapsulate the entire stopping distance either, since stopping distance is a broader measure that includes standard braking scenarios, not just emergencies.

Thus, the choice highlighting the distance from the moment the brakes begin to work until the vehicle stops precisely defines stopping distance.