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AQA · GCSE · Combined Science · Higher

Reaction time and thinking distance

Q06.1 2 marks

Figure 8 shows the distance-time graph for a car travelling at 15 m/s15\ \mathrm{m/s}.

Distance-time graph for a car travelling at constant speed. The x-axis is time in seconds from 0 to 1.0. The y-axis is distance in metres from 0 to 15. A straight line runs from 0 m at 0 s to 15 m at 1.0 s.

Figure 8

Enlarged question image

Distance-time graph for a car travelling at constant speed. The x-axis is time in seconds from 0 to 1.0. The y-axis is distance in metres from 0 to 15. A straight line runs from 0 m at 0 s to 15 m at 1.0 s.
Figure 8

When the driver is tired, his reaction time increases from 0.50 s0.50\ \mathrm{s} to 0.82 s0.82\ \mathrm{s}. Determine the extra distance the car would travel before the driver starts braking.

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Marking points

  1. 1 Find the increase in reaction time, 0.82−0.50=0.32 s0.82-0.50=0.32\ \mathrm{s}, or use the graph to find the two corresponding distances.
  2. 2 Calculate the extra distance as 15×0.32=4.8 m15\times0.32=4.8\ \mathrm{m}, or subtract the graph distances to get about 4.8 m4.8\ \mathrm{m}.

Full-mark answer

The reaction time increases by 0.82−0.50=0.32 s0.82-0.50=0.32\ \mathrm{s}. At 15 m/s15\ \mathrm{m/s}, the extra distance is 15×0.32=4.8 m15\times0.32=4.8\ \mathrm{m}.

Why this answer loses marks

15×0.82=12.3 m15\times0.82=12.3\ \mathrm{m}

This gives the full thinking distance for the tired driver, not the extra distance compared with 0.50 s0.50\ \mathrm{s}.

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