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AS Daily A Level Physics question

2026-01-25 OCR A Forces and motion (Module 3): Dynamics, drag and terminal velocity OCR-A Physics A (H156) Module 3: Forces and motion — Newton’s laws of motion (AS) OCR-A Physics A (H156) Module 3: Forces in action — Drag and terminal velocity (AS)

A lightweight coffee filter is dropped from rest and soon falls at a steady terminal velocity through air. Which statement must be true at terminal velocity?

  1. A Its weight is smaller than the drag force, so it moves at steady speed.
  2. B There is no air resistance acting because the speed is constant.
  3. C There is a small downward resultant force, which keeps the speed constant.
  4. D The upward drag is equal to the weight; the resultant force and acceleration are zero. (correct)

Answer

The correct answer is D.

Correct: D — The upward drag is equal to the weight; the resultant force and acceleration are zero. A This wrongly suggests drag must exceed weight to keep speed steady; if drag were larger, the coffee filter would slow down. B Constant speed means zero resultant force, not zero air resistance; drag must be present to balance weight. C Any non-zero resultant force would cause acceleration, so speed would change rather than stay constant. D At terminal velocity, opposing forces balance exactly, giving zero resultant and zero acceleration.

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