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A2 Daily A Level Physics question

2026-05-19 OCR A Dynamics: forces, terminal velocity; friction & drag (qualitative) Module 3: Forces and motion — 3.2 Forces in action (fluid friction, drag and terminal velocity) Module 3: Forces and motion — 3.5 Newton’s laws of motion (equilibrium at terminal speed)

A skydiver of fixed mass descends at terminal speed with a medium parachute. They then switch to a larger parachute with four times the canopy area; air density and conditions are unchanged. Assuming air resistance is proportional to cross-sectional area and to the square of speed, what happens to the terminal speed?

  1. A It halves (v_new = 0.5 v_old). (correct)
  2. B It quarters (v_new = 0.25 v_old).
  3. C No change (v_new = v_old).
  4. D It doubles (v_new = 2 v_old).

Answer

The correct answer is A.

Correct: A — It halves (v_new = 0.5 v_old). At terminal speed, weight equals drag; with drag proportional to area and to speed squared, quadrupling area means A·v^2 must stay the same, so v falls by √4 = 2. A This matches the required change: v_new = v_old/√4 = v_old/2. B This assumes a linear-in-speed drag (A·v), so it would underpredict drag; quartering v with 4× area gives only 1/4 of the needed drag. C This ignores that terminal speed depends on drag factors (area, shape) as well as weight. D Increasing area increases drag for a given speed, so the balancing terminal speed must decrease, not increase.

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