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AS Daily A Level Physics question

2026-04-17 OCR A Dynamics: forces, terminal velocity; friction & drag (qualitative) (Module 3) Module 3.2 Forces in Action — drag and terminal velocity Module 3.5 Newton’s laws — equilibrium of forces (qualitative)

A skydiver falls at terminal speed v1 in a compact posture. They then spread out so their frontal area doubles, with mass and air conditions unchanged. The resistive force from the air increases with speed and frontal area. Which statement must be true about the new terminal speed v2 compared with v1?

  1. A v2 is double v1 because a larger area pushes more air downward
  2. B v2 is half of v1 because doubling area halves the speed needed
  3. C v2 is the same as v1 because the weight has not changed
  4. D v2 is about 0.71 of v1 because doubling area reduces terminal speed by a factor of √2 (correct)

Answer

The correct answer is D.

Correct: D — v2 is about 0.71 of v1 because doubling area reduces terminal speed by a factor of √2. At terminal speed, weight is balanced by drag; if area doubles while weight is unchanged, speed must fall so that area × speed^2 stays the same, giving v2/v1 = 1/√2 ≈ 0.71. A assumes terminal speed increases with area, but a larger area increases drag at a given speed, so the terminal speed falls, not rises. B assumes a linear inverse relationship with area; because drag depends on speed squared, the speed scales with the square root, not directly with area. C ignores the role of area in the drag balance; even though weight is unchanged, changing area changes the terminal speed.

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