Which of these statements about speed management and braking is true?
A. The total stopping distance of a bus is the distance it takes to stop once the brakes are put on.
B. Stopping time increases one second for each 10 mph over 20 mph.
C. you need about four times as much stopping distance at 40 mph as at 20 mph.
The Correct Answer and Explanation is :
The correct statement about speed management and braking is C: you need about four times as much stopping distance at 40 mph as at 20 mph.
Explanation:
Understanding stopping distances is crucial for safe driving, particularly for larger vehicles like buses. Stopping distance is composed of two key components: reaction distance and braking distance.
- Reaction Distance: This is the distance a vehicle travels while the driver reacts to a hazard. It depends on the driver’s perception time and the vehicle’s speed. As speed increases, the reaction distance also increases. For instance, at 20 mph, the reaction distance may be around 20 feet; at 40 mph, it could be around 40 feet.
- Braking Distance: This is the distance required to stop the vehicle once the brakes are applied. The braking distance increases with the square of the speed. This means that if you double your speed, the braking distance does not just double; it quadruples. For example, if a bus takes 20 feet to stop from 20 mph, it would require approximately 80 feet to stop from 40 mph.
Combining these two distances gives the total stopping distance. At 20 mph, the total stopping distance might be around 40 feet (20 feet reaction + 20 feet braking), while at 40 mph, it could increase to about 160 feet (40 feet reaction + 120 feet braking). This illustrates that at higher speeds, stopping distances grow significantly, emphasizing the need for careful speed management.
In summary, due to the quadratic relationship between speed and braking distance, you do indeed need approximately four times as much stopping distance at 40 mph as you do at 20 mph, making option C the correct choice.