AS Daily A Level Physics question
A motion sensor records a straight-line displacement–time graph through the origin for a student walking directly away from the sensor at constant speed. On a second trial the student walks in the same direction at double the speed and starts 2.0 m further from the sensor than before. Which statement must be true about the second graph compared with the first?
Answer
The correct answer is B.
Correct: B — B The gradient is doubled, and the line is shifted up by 2.0 m. Doubling speed doubles the gradient of a displacement–time graph, and starting 2.0 m further away increases the y-intercept by 2.0 m. A The gradient cannot stay the same if the speed is doubled; the intercept shift alone does not account for the higher speed. B This is correct because gradient ∝ speed and the starting displacement increases by 2.0 m. C The intercept should increase (shift up) when starting further away, not decrease. D Doubling speed does not halve the gradient, and there is no reason for only a 1.0 m shift when the start is 2.0 m further away.