Analysing vehicle stopping distances

This is what a velocity-time graph represents. It helps you calculate reaction time and the time it takes for a vehicle to stop.

A velocity-time graph of stopping distances. A rectangular area is coloured purple to represent the thinking distance. A triangular area is coloured blue to represent the braking distance.

Look at the graph and answer the questions.

A speed-time graph. The line starts at speed 15 meters per second at time 0. It continues at the same speed until time 1 second. The line then continues to speed 0 at time 4 seconds.
Question

What is the driver’s reaction time?

0.8 s

Question

What was the speed of the vehicle before it started to brake?

15 m/s

Question

What distance was travelled while the driver was reacting (the thinking distance)?

The area under the flat part of the graph, which is 15 m/s × 0.8 s = 12 m.

Question

How long did it take the car to stop?

The time between 0.8 s and 4 s = 3.2 s.

Question

What is the braking distance?

The area of the triangle.

½ × base × height = ½ × 3.2 s × 15 m/s = 24 m

Question

What is the total stopping distance?

12 m + 24 m = 36 m