A ball is thrown horizontally and travels in a curved path before hitting the ground. Explain why the ball's velocity is changing throughout its flight, even though no horizontal force acts on it.

AQA GCSE Physics (8463) — 4.5.6 Forces and motion · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A ball is thrown horizontally from a raised platform. It follows a curved path and lands on the ground some distance away.

Model answer (4 marks)

1. Velocity is a vector, having both magnitude and direction.
2. The ball is acted on by gravity, a downward force.
3. This force gives a downward acceleration, adding a vertical component to the velocity.
4. As the direction of the velocity vector changes continuously, the velocity changes even though the horizontal speed remains constant.

Examiner tips

  • Use the term ‘velocity is a vector’ to earn the first point. Show that gravity gives a downward acceleration. Explain that the vertical component changes the direction of the velocity vector. Keep the answer concise – 4 short sentences is enough for full marks.

Common mistakes

  • Saying the ball’s speed changes, not its velocity. Forgetting to mention that gravity acts on the ball. Ignoring that the velocity vector’s direction changes, not just its magnitude.

Mark scheme (4 marks)

  1. Velocity is a vector quantity, so it has both magnitude and direction
  2. Gravity / weight acts downward on the ball, causing a downward acceleration
  3. The downward force produces a resultant force, so the ball accelerates downwards / gains a downward component of velocity
  4. The direction of the overall velocity changes continuously, so the velocity changes even if horizontal speed stays constant

Key terms in this question

velocity

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