Question Constellation Sign up for free AQA · GCSE · Combined Science · Higher
Vehicle mass and stopping distance
Figure 12 shows a delivery van full of packages.
The driver delivers all the packages. The empty van has a shorter stopping distance than the full van when driven at the same speed. Explain why.
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Marking points
- 1 State that the brakes can apply the same maximum braking force to the van.
- 2 Link the lower mass of the empty van to a greater deceleration for the same braking force.
- 3 Conclude that the greater deceleration gives a shorter braking distance.
- 4 Alternatively, state that the empty van has less kinetic energy than the full van at the same speed.
- 5 Alternatively, explain that less work is needed to bring the empty van to a stop.
- 6 Alternatively, link the same braking force to a shorter braking distance because less work is needed.
Full-mark answer
The brakes can apply the same maximum braking force, but after the packages are delivered the van has less mass. For the same braking force, the empty van has a greater deceleration, so it stops in a shorter distance.
Why this answer loses marks
The empty van has less kinetic energy.
This can gain credit for the alternative energy route, but it needs the further link that less work is needed and the same braking force gives a shorter distance.