A tennis ball is dropped from rest at the top of a tall building. It falls downward, speeding up before hitting the ground. Describe the motion of the tennis ball from the moment it is released until it hits the ground, and explain how the forces acting on it change during this time.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A tennis ball is held stationary at the top of a tall building and then released. The ball falls through the air and hits the ground several seconds later.
Model answer (5 marks)
The ball starts from rest, so its initial velocity is 0 m s⁻¹. Once released it accelerates downward, gaining speed as it falls. The only force that always acts on it is its weight, mg, directed downwards. As the ball speeds up, air resistance (drag) grows in magnitude and acts upward. The upward drag reduces the net downward force, so the acceleration is less than g, although the ball still speeds up. The motion continues until the ball reaches the ground.
Examiner tips
- Use the exact terms ‘initial velocity’, ‘accelerates’, ‘weight’, ‘air resistance’, ‘net force’, ‘decreases acceleration’.
- Show the sequence: start from rest → acceleration → increasing drag → reduced net force → still speeding up.
- Keep the answer concise and to the point, matching the 5 marks.
Common mistakes
- Writing that the ball’s speed decreases instead of increases.
- Forgetting to mention that air resistance grows as speed increases.
- Using vague phrases like ‘forces change’ without specifying which forces and how.
Mark scheme (5 marks)
- The ball starts from rest / has zero velocity at the moment of release.
- The ball accelerates / speeds up as it falls.
- Weight / gravitational force acts downward on the ball throughout the fall.
- Air resistance / drag acts upward on the ball and increases as the ball speeds up.
- As air resistance increases, the resultant force decreases, so the acceleration decreases (the ball still speeds up but more slowly).
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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