A skydiver jumps from an aircraft and falls vertically downward. At first, the skydiver accelerates. After some time, the skydiver reaches terminal velocity. Explain why the skydiver first accelerates and then reaches terminal velocity.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A skydiver of weight 800 N jumps from an aircraft and falls vertically downward through the air.
Model answer (5 marks)
The skydiver’s weight (800 N) acts downward.
1. At the instant of the jump the air resistance is small, so the downward weight exceeds the upward drag.
2. The unbalanced resultant force is therefore downward.
3. By Newton’s second law a resultant force causes acceleration, so the skydiver speeds up.
4. As the speed increases the drag force increases (∝v²).
5. When the drag equals the weight the resultant force becomes zero and the skydiver reaches terminal velocity, moving at constant speed.
1. At the instant of the jump the air resistance is small, so the downward weight exceeds the upward drag.
2. The unbalanced resultant force is therefore downward.
3. By Newton’s second law a resultant force causes acceleration, so the skydiver speeds up.
4. As the speed increases the drag force increases (∝v²).
5. When the drag equals the weight the resultant force becomes zero and the skydiver reaches terminal velocity, moving at constant speed.
Examiner tips
- Use the exact terms ‘weight’, ‘air resistance’, ‘resultant force’, ‘unbalanced’, ‘Newton’s second law’, and ‘terminal velocity’.
- Show the sequence: weight > drag → acceleration → drag ↑ with speed → drag = weight → zero resultant → constant speed.
Common mistakes
- Confusing drag with weight or saying the skydiver ‘stops’ instead of ‘moves at constant speed’.
- Omitting the step that drag increases with speed or the fact that the resultant force becomes zero at terminal velocity.
Mark scheme (5 marks)
- Weight (gravitational force) acts downward on the skydiver
- At the start, air resistance (drag) is less than the weight, so there is a resultant force downward
- A resultant (unbalanced) force causes the skydiver to accelerate (Newton's second law / resultant force causes acceleration)
- As the skydiver's speed increases, air resistance (drag) increases
- At terminal velocity, air resistance equals weight, so the resultant force is zero and the skydiver moves at constant velocity
Key terms in this question
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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