Fig. 1 shows a speed-time graph produced by a motion sensor on an electric tram. The tram leaves a station, moves along a straight track, and then brakes be...
Question 1 Report
Fig. 1 shows a speed-time graph produced by a motion sensor on an electric tram. The tram leaves a station, moves along a straight track, and then brakes before the next platform. Point P is at 20 s. The driver keeps passengers comfortable by avoiding sudden changes in velocity. The graph uses speed rather than velocity because the tram does not reverse direction during this journey.
(a) Name the type of graph shown in Fig. 1. [1]
(b) Describe the tram's motion between point P and the start of braking. [2]
(c) What does the downward sloping line show about the tram's speed? [2]
(d) Give the equation linking acceleration, change in velocity and time. [2]
(e) Explain why passengers move forwards relative to the tram when it brakes. [3]
Answer Details
- (a) This is a speed-time graph. [1]
- (b) Between P and the start of braking, the tram travels at constant speed. The horizontal line shows that speed is not changing. [2]
- (c) The downward straight line shows that speed decreases at a constant rate: the tram decelerates. [2]
- (d) \[\text{acceleration}=\frac{\text{change in velocity}}{\text{time}}\] \[a=\frac{v-u}{t}\] [2]
- (e) Passengers have inertia, so their bodies tend to continue moving forwards at their previous velocity. When the tram slows beneath them, they move forwards relative to the tram. [3]
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