AQA GCSE Physics Foundation (8463), Foundation tier · Forces › Forces and motion › Forces and braking
Practise Stopping distance. 6 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
The stopping distance of a vehicle is the thinking distance plus the braking distance. You need to know what affects each part, how speed affects stopping distance, and how to calculate stopping distances from data. If you take GCSE Physics (not Combined Science), you also need to interpret graphs of stopping distance against speed for different vehicles.
For a given braking force, the greater the speed of the vehicle, the greater the stopping distance.
Thinking distance = speed × reaction time. For the same reaction time, thinking distance is directly proportional to speed: double the speed, double the thinking distance.
So at higher speeds, the braking distance makes up a bigger share of the stopping distance.
What affects each part
Thinking distance depends on the speed and on the driver's reaction time, which is increased by tiredness, drugs, alcohol and distractions.
Braking distance depends on the speed, the road and weather conditions (wet or icy), the condition of the brakes and tyres, and the mass of the vehicle.
Graphs of stopping distance against speed
diagram
A graph of thinking distance against speed is a straight line through the origin (for a constant reaction time).
A graph of braking distance against speed is a curve that gets steeper, because braking distance increases faster than speed.
Graphs for different vehicles can be compared by reading each line at the same speed. For example, a heavily loaded lorry usually has a greater stopping distance than a car at the same speed, so it needs a bigger gap to the vehicle in front.
How to answer each type of question
Calculate a stopping distance
3 marksGrade 5
Thinking distance = speed × reaction time.
Add the braking distance.
Give the answer in m.
Example. A driver is travelling at 15 m/s. Her reaction time is 0.60 s. The braking distance of her car is 17 m. Calculate the stopping distance.
Thinking distance depends on the driver; braking distance depends on the vehicle and the road.
Exam technique
Always say which part of the stopping distance a factor affects: thinking or braking.
If you are given a speed and a reaction time, calculate the thinking distance with s = v t.
When evaluating data or a graph, quote numbers from it to support your answer.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Define stopping distance as thinking plus brakingThinking distance is covered during the reaction time; braking distance is covered while the brakes act.
Grade 4
Calculate stopping distance from given dataAdd the thinking distance and the braking distance.
Grade 5
Calculate thinking distance using s = v tThinking distance = speed × reaction time.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
What is meant by the braking distance of a car?
The distance travelled under the braking force.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) What is meant by the thinking distance of a car? Tick (✓) one box.[1]
The distance travelled during the driver’s reaction time
The distance travelled while the brakes are applied
The total distance needed to stop
The distance between the car and the car in front
(b) What is meant by the braking distance of a car?[1]
(c) A car has a thinking distance of 12 m and a braking distance of 24 m. Calculate the stopping distance of the car.[1]
(d) For a given braking force, how does the stopping distance change if the speed of the car increases?[1]
Show the answer and mark scheme
(a)Answer: The distance travelled during the driver’s reaction time
(b)Answer: The distance travelled under the braking force.
the distance the car travels under the braking force (after the brakes are applied)
(c)Answer: 36 m
36 (m)
(d)Answer: It increases.
it increases
Question 2Medium4 marks
A driver travels at 24 m/s with a reaction time of 0.65 s.
(a) Calculate the driver’s thinking distance.[2]
(b) The driver is using a hands-free phone, which increases their reaction time to 0.90 s. Calculate the increase in thinking distance this causes.[2]
Show the answer and mark scheme
(a)Answer: 15.6 m
s = 24 × 0.65
15.6 (m)
(b)Answer: 6.0 m
increase in reaction time = 0.90 − 0.65 = 0.25 (s)