A car is travelling at high speed along a motorway when the driver notices a hazard ahead and applies the brakes. The car comes to a complete stop. Explain how the thinking distance and the braking distance each contribute to the total stopping distance, and describe TWO factors — one that affects thinking distance and one that affects braking distance — that could increase the total stopping distance.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
The total stopping distance is the sum of the thinking distance and the braking distance.
Thinking distance is the distance the car travels while the driver is reacting to the hazard – it depends on the driver’s reaction time. Braking distance is the distance travelled after the brakes are applied until the car stops – it depends on the braking force and the vehicle’s speed.
A factor that increases thinking distance is tiredness, which lengthens reaction time. A factor that increases braking distance is wet road conditions, which reduce tyre grip and increase the distance needed to stop.
Thinking distance is the distance the car travels while the driver is reacting to the hazard – it depends on the driver’s reaction time. Braking distance is the distance travelled after the brakes are applied until the car stops – it depends on the braking force and the vehicle’s speed.
A factor that increases thinking distance is tiredness, which lengthens reaction time. A factor that increases braking distance is wet road conditions, which reduce tyre grip and increase the distance needed to stop.
Examiner tips
- State that stopping distance = thinking + braking distance; explain each; give one factor for each; keep answer concise and use exam terminology.
Common mistakes
- Confusing thinking distance with braking distance; not naming a specific factor; using vague terms like ‘slow’ instead of ‘tiredness’ or ‘wet road’.
Mark scheme (5 marks)
- Stopping distance is the sum of thinking distance and braking distance
- Thinking distance is the distance the car travels during the driver's reaction time
- Braking distance is the distance the car travels under the braking force (after brakes are applied until the car stops)
- A named factor that increases thinking distance — e.g. tiredness, alcohol, or drugs (increasing reaction time)
- A named factor that increases braking distance — e.g. adverse road/weather conditions (e.g. wet or icy roads) or poor vehicle condition (e.g. worn brakes or worn tyres)
Key terms in this question
stopping distance · thinking distance · braking distance
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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