Final answer:
A safe following distance can be determined using the concept of reaction time and stopping distance. For speeds up to 55 mph, a safe following distance of 3 seconds is recommended.
Step-by-step explanation:
A safe following distance can be determined using the concept of reaction time and stopping distance. The equation for stopping distance is given by:
Stopping distance = reaction distance + braking distance
The reaction distance is the distance covered by a vehicle during the driver's reaction time, which is usually around 1-2 seconds. The braking distance is the distance covered by a vehicle while it's slowing down to a stop. For speeds up to 55 mph, a safe following distance of 3 seconds is recommended. Therefore, the answer would be 55 mph.