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.
Look at the graph and answer the questions.
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