A passenger is travelling on a bus that performs an emergency stop. The passenger, who is not wearing a seat belt, is thrown forwards and hits the seat in front. Explain why the passenger continues to move forwards when the bus stops suddenly, and describe how wearing a seat belt would reduce the risk of injury in this situation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The passenger keeps moving forward because of inertia – they tend to remain in their state of motion.
The bus decelerates, but no force acts on the passenger to stop them at the same rate.
A seat belt applies a force to the passenger, decelerating them with the bus and stopping the forward motion.
The belt stretches slightly, increasing the time over which the passenger decelerates, which reduces the force on the passenger and therefore the risk of injury.
The bus decelerates, but no force acts on the passenger to stop them at the same rate.
A seat belt applies a force to the passenger, decelerating them with the bus and stopping the forward motion.
The belt stretches slightly, increasing the time over which the passenger decelerates, which reduces the force on the passenger and therefore the risk of injury.
Examiner tips
- Use the word "inertia" to explain the initial motion. Show the sequence: bus decelerates → passenger continues → seat belt applies force. Mention the belt’s slight stretch to justify the reduced force.
- Include the key terms: inertia, deceleration, force, time, risk of injury.
Common mistakes
- Confusing the passenger’s motion with the bus’s motion. Forgetting to mention the belt’s stretch and the increased deceleration time. Using vague phrases like "the belt stops them" without explaining the force or time aspect.
Mark scheme (4 marks)
- The passenger continues to move forwards because of inertia / they tend to remain in their state of motion
- The bus decelerates / stops but no force acts on the passenger to stop them at the same rate
- The seat belt applies a force to the passenger to decelerate them with the bus / stops the passenger moving forwards
- The seat belt stretches / extends slightly, increasing the time over which the passenger decelerates, reducing the force on the passenger / reducing the risk of injury
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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