AS Daily A Level Physics question
A toy car moves in a straight line on a bench. Its displacement s from the start (positive to the right) is plotted against time t as three straight segments: from 0–4 s, s increases uniformly from 0 m to +8 m; from 4–7 s, s stays constant at +8 m; from 7–10 s, s decreases uniformly from +8 m to +2 m. Which statement must be true?
Answer
The correct answer is C.
Correct: C — C Over 0–10 s, the average speed is greater than the magnitude of the average velocity. A Straight segments indicate constant velocity only within each segment, and the horizontal part shows zero speed, so the speed is not constant for the whole motion. B Moving back towards the start does not guarantee returning to s = 0; the car finishes with a positive displacement. C This is correct because total distance travelled exceeds the net change in position, so average speed (scalar) is larger than the magnitude of average velocity (vector based on displacement). D Zero velocity is indicated by a horizontal section (zero gradient) on a displacement–time graph, not by the displacement being zero.