A firefighter wearing a heavy backpack jumps from a stationary helicopter and lands on a rooftop. Describe what happens to the momentum of the firefighter from the moment they leave the helicopter until the moment they come to rest on the rooftop. Refer to the forces acting throughout.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A firefighter wearing a heavy backpack steps out of a stationary helicopter hovering above a building. The firefighter falls and lands on the rooftop, coming to rest.
Model answer (4 marks)
The firefighter has zero momentum when they leave the stationary helicopter.
A resultant downward force (their weight) acts on the firefighter, so their momentum changes and increases in the downward direction.
As the firefighter falls, the downward force continues to act, giving a rate of change of momentum and increasing the magnitude of the downward momentum.
When the firefighter lands, an upward force from the rooftop acts, reducing the downward momentum to zero and bringing the firefighter to rest.
A resultant downward force (their weight) acts on the firefighter, so their momentum changes and increases in the downward direction.
As the firefighter falls, the downward force continues to act, giving a rate of change of momentum and increasing the magnitude of the downward momentum.
When the firefighter lands, an upward force from the rooftop acts, reducing the downward momentum to zero and bringing the firefighter to rest.
Examiner tips
- Use the word "momentum" and specify direction (downward/upward).
- Show the sequence: zero → increasing downward → reduced to zero by upward force.
- Mention the forces (weight, rooftop reaction) explicitly.
Common mistakes
- Confusing velocity with momentum; forgetting to state initial zero momentum.
- Omitting the upward force from the rooftop or describing it as a friction force instead of a normal reaction.
Mark scheme (4 marks)
- The firefighter has zero momentum when they leave the stationary helicopter
- A resultant downward force (weight / gravity) acts on the firefighter, causing a change in momentum / increasing momentum
- As the firefighter falls, momentum increases in the downward direction because the force causes a rate of change of momentum
- On landing, a resultant upward force from the rooftop acts on the firefighter, reducing momentum to zero / bringing the firefighter to rest
Key terms in this question
Related
- All AQA GCSE Physics (8463) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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