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AS Daily A Level Physics question

2025-09-25 OCR A Foundations of physics (M2): Scalars and vectors; units, Forces and motion (M3): Kinematics — displacement–time graphs 3.1.1(a) 3.1.1(c)

Two walkers move in a straight line along a path. From t = 0 s to t = 8 s, their motions are straight lines on displacement–time graphs: Walker P goes from (0 s, 0 m) to (8 s, +24 m); Walker Q goes from (0 s, 0 m) to (8 s, −12 m). Which statement must be true?

  1. A Walker P's average speed is twice Walker Q's. (correct)
  2. B Both have the same average speed because both graphs are straight lines.
  3. C Walker Q's speed is negative because the graph slopes downward.
  4. D Their average velocities have equal magnitude but opposite direction.

Answer

The correct answer is A.

Correct: A — Walker P's average speed is twice Walker Q's. A: Speeds are the magnitudes of gradients, so |24 m|/8 s = 3.0 m/s and |−12 m|/8 s = 1.5 m/s, giving a 2:1 ratio. B: Straight lines indicate constant velocity, not equal speed; the different gradients show different speeds. C: Speed is a scalar and cannot be negative; the downward slope indicates a negative velocity (direction), not negative speed. D: The magnitudes of the average velocities are not equal: 3.0 m/s for P versus 1.5 m/s for Q.

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