AQA · GCSE · Combined Science · Higher

Driver’s reaction time calculation

Q06.1 3 marks

The distance a car travels during the driver’s reaction time is called the thinking distance. Figure 9 shows how thinking distance depends on speed for a car.

Line graph titled Figure 9. The y-axis is thinking distance in metres from 0 to 25. The x-axis is speed of car in metres per second from 0 to 35. A straight line starts at 0 m at 0 m/s and rises to about 21 m at 30 m/s. — Figure 9

Determine the driver’s reaction time. Use the Physics Equations Sheet.

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Marking points

1 Use a correct pair of values from the graph, such as thinking distance $21\ \mathrm{m}$ at speed $30\ \mathrm{m/s}$ .
2 Rearrange or substitute into $\text{distance}=\text{speed}\times\text{time}$ to find $t=\frac{21}{30}$ .
3 Give the reaction time as $0.7\ \mathrm{s}$ , or $0.70\ \mathrm{s}$ .

Full-mark answer

From the graph, at $30\ \mathrm{m/s}$ the thinking distance is about $21\ \mathrm{m}$ . Using $\text{distance}=\text{speed}\times\text{time}$ , $21=30t$ , so $t=\frac{21}{30}=0.7\ \mathrm{s}$ .

Why this answer loses marks

$21\times30=630\ \mathrm{s}$

The equation has not been rearranged to make time the subject.

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