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AS Daily A Level Physics question

2025-10-30 OCR A Mechanics & Materials (M3) 3.2.2(b) 3.2.2(d)(i)

A lab demo uses two identical toy parachutes with the same canopy area and shape. Parachute B carries a payload twice the mass of parachute A. In this speed range, air resistance on each canopy is roughly proportional to the square of the speed and to the canopy area. After falling long enough, both reach terminal speed. Compared with A, what is B’s terminal speed?

  1. A About 1.4 times larger than A’s, because the drag must double to balance twice the weight. (correct)
  2. B Twice A’s, because terminal speed is proportional to mass for the same area.
  3. C The same as A’s, because both have the same canopy area and shape.
  4. D Smaller than A’s, because the heavier payload reaches the balance of forces at a lower speed.

Answer

The correct answer is A.

Correct: A — About 1.4 times larger than A’s, because the drag must double to balance twice the weight. At terminal speed, drag equals weight; with the same area and shape, drag varies with speed squared, so doubling weight requires v to increase by √2 ≈ 1.4. A This states the correct √2 scaling from drag balancing twice the weight. B Assumes terminal speed is directly proportional to mass; it’s proportional to the square root of mass when area and shape are fixed. C Ignores that a heavier payload needs a larger drag to balance weight; with the same area, that requires a higher speed, not the same speed. D Reverses the dependence: a greater weight needs a higher speed to generate the larger drag, not a lower speed.

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