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Maximum Deceleration from Graph Gradient
Figure 12 shows a velocity–time graph for a train travelling between two stations.
Determine the maximum deceleration of the train.
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Marking points
- 1 Chooses the steepest deceleration section.
- 2 Calculates the gradient from appropriate graph values.
- 3 Gives the maximum deceleration as 0.3 m/s² in magnitude.
Full-mark answer
The steepest deceleration is from 600 s to 720 s, where velocity falls from 56 m/s to 20 m/s. a = Δv/Δt = (20 − 56)/(720 − 600) = −36/120 = −0.3 m/s², so the maximum deceleration is 0.3 m/s².
Why this answer loses marks
Uses the gradient across the whole braking region.
Maximum deceleration requires the steepest individual section, not an average across sections with different slopes.