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AS Daily A Level Physics question

2025-12-30 OCR A Kinematics: displacement–time graphs (Module 3.1) 3.1.1(a) 3.1.1(b) 3.1.1(c)

In a lab, a trolley moves along a straight track while a motion sensor records its displacement s from a fixed marker against time t. The graph consists of three straight sections: from 0–20 s it is a straight line with gradient +0.80 m s^-1; from 20–30 s it is horizontal; from 30–50 s it is a straight line with gradient −0.40 m s^-1. Which statement is correct?

  1. A Final displacement from the marker is 0 m because the return leg cancels the outward leg.
  2. B Total distance travelled is 16 m; the 10 s stop and the return do not add to the distance.
  3. C Average speed over 0–50 s is 0.48 m s^-1 and average velocity is 0.16 m s^-1 away from the marker. (correct)
  4. D The trolley accelerates during the first and last sections because the velocity changes sign overall.

Answer

The correct answer is C.

Correct: C — Average speed over 0–50 s is 0.48 m s^-1 and average velocity is 0.16 m s^-1 away from the marker. A It is not 0 m: displacement = (+0.80×20) + 0 + (−0.40×20) = +8 m from the marker. B Distance is not 16 m: total distance = 16 + 0 + 8 = 24 m (stopping adds zero, returning adds 8 m). C Using totals, average speed = 24/50 = 0.48 m s^-1 and average velocity = +8/50 = 0.16 m s^-1 away from the marker. D The straight segments have constant gradients (constant velocities), so acceleration is zero within them; the sign change occurs between segments, not as acceleration during them.

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