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AS Daily A Level Physics question

2026-07-10 OCR A Kinematics — displacement–time graphs (Mechanics, Module 3) OCR A Module 3.1 Kinematics: displacement–time graphs; velocity as gradient OCR A Module 3.1 Kinematics: average speed vs average velocity

In a lab, a motion sensor tracks a trolley moving along a straight track. Its displacement–time graph is piecewise linear: from t = 0 s to t = 12 s the displacement increases uniformly from 0 m to +24 m; from t = 12 s to t = 20 s the displacement stays constant at +24 m; from t = 20 s to t = 28 s the displacement decreases uniformly back to 0 m. Which statement must be true?

  1. A The average velocity from 0 s to 28 s is +1.7 m/s.
  2. B The speed on the return segment is 1.5 times the outward speed. (correct)
  3. C The trolley’s speed at t = 16 s is 1.7 m/s.
  4. D The average speed from 0 s to 28 s is 2.4 m/s.

Answer

The correct answer is B.

Correct: B — The speed on the return segment is 1.5 times the outward speed. A confuses average velocity with average speed: over the whole trip the final displacement equals the initial, so the average velocity is 0 m/s, not +1.7 m/s. B is correct because outward speed = 24 m / 12 s = 2.0 m/s and return speed = 24 m / 8 s = 3.0 m/s, so the ratio is 3.0/2.0 = 1.5. C is wrong because at t = 16 s the graph is flat (t = 12–20 s), so the speed is 0 m/s, not 1.7 m/s. D is wrong because the average speed is total distance / total time = 48 m / 28 s ≈ 1.7 m/s; 2.4 m/s incorrectly ignores the waiting period.

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