What is the stopping distance at 20 mph?

What is the stopping distance at 20 mph?

• A. 23 metres
• B. 36 metres
• C. 53 metres
• D. 12 metres

Answer: (D)

Stopping distance is made up of two parts: thinking distance (the distance you travel while you react) and braking distance (the distance you travel after you start braking until you stop). At 20 mph (about 9 m/s), use a typical reaction time of around 0.7 seconds. Thinking distance ≈ 9 × 0.7 ≈ 6 metres. Braking distance on a dry road at this speed is also roughly about 6 metres. Add them together and you get about 12 metres in total. So the stopping distance at 20 mph is approximately 12 metres, assuming dry road and normal reaction time.

Stopping distance is made up of two parts: thinking distance (the distance you travel while you react) and braking distance (the distance you travel after you start braking until you stop). At 20 mph (about 9 m/s), use a typical reaction time of around 0.7 seconds. Thinking distance ≈ 9 × 0.7 ≈ 6 metres. Braking distance on a dry road at this speed is also roughly about 6 metres. Add them together and you get about 12 metres in total. So the stopping distance at 20 mph is approximately 12 metres, assuming dry road and normal reaction time.