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AS Daily A Level Physics question

2026-01-08 OCR A Dynamics: terminal velocity; drag (qualitative) 3.2.2(d)(i)

Which statement must be true when a falling raindrop has reached terminal velocity in still air?

  1. A The resultant force is upward because air resistance overtakes the weight at high speed.
  2. B The weight remains larger than the drag, so the drop still speeds up a little.
  3. C The upward drag equals the weight, so the acceleration is zero. (correct)
  4. D Both the drag and the weight are zero, so the speed stays constant.

Answer

The correct answer is C.

Correct: C — The upward drag equals the weight, so the acceleration is zero. A The resultant is not upward at terminal speed; if it were, the drop would slow down rather than continue at constant speed. B If weight were greater than drag, there would be a net downward force and the drop would still be accelerating, so not at terminal velocity. C Balanced forces mean zero resultant and hence zero acceleration, giving constant speed. D Weight cannot be zero; at terminal velocity the forces are present and equal in magnitude, not absent.

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