Thinking & Braking Distances (AQA GCSE Combined Science: Trilogy: Physics): Revision Note
Exam code: 8464
Thinking & Braking Distances
The stopping distance of a car is defined as:
The total distance travelled during the time it takes for a car to stop in response to some emergency
It can be written as an equation involving two distances:
Stopping distance = Thinking distance + Braking distance
Where:
Thinking distance = the distance travelled in the time it takes the driver to react (reaction time) in metres (m)
Braking distance = the distance travelled under the braking force in metres (m)
Stopping distance = the sum of the thinking distance and braking distance, in metres (m)
For a given braking force, the greater the speed of the vehicle, the greater the stopping distance
Worked Example
At a speed of 20 m/s, a particular vehicle had a stopping distance of 40 metres. The car travelled 14 metres whilst the driver was reacting to the incident in front of him. What was the braking distance?
A. 54 m
B. 34 m
C. 26 m
D. 6 m
Answer: C
Step 1: Identify the different variables
Stopping distance = 40 m
Thinking distance = 14 m
Step 2: Rearrange the formula for stopping distance
Stopping distance = Thinking distance + Braking distance
Braking distance = Stopping distance – Thinking distance
Step 3: Calculate and identify the correct braking distance
Braking distance = 40 – 14 = 26 metres
Therefore, the answer is C
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