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Vehicle motion for AQA GCSE Physics

Vehicle motion

This page covers the following topics:

1. Thinking distance
2. Reaction time
3. Breaking distance
4. Stopping distance

The thinking distance is the distance travelled by the driver during the time it takes for them to react to a hazardous situation and apply the brakes. The greater the reaction time of the driver, the greater the thinking distance and the greater the car's speed, the greater the thinking distance. Some factors which affect the thinking distance are being tired, being under the influence of alcohol or drugs and being distracted.

Thinking distance

The reaction time is the time between a driver noticing a hazardous situation ahead and applying brakes. The factors that affect reaction time are the same as those that affect thinking distance, due to the fact that thinking distance is determined by reaction time.

Reaction time

When the brakes are applied, work is done to stop the car by the frictional force of the brakes on the tyres, thus reducing the car's kinetic energy and bringing it to a stop. The braking distance is the distance travelled by the car after the brakes are applied until the car stops. The braking distance will be greater if there are poor tyres, brakes or road conditions. The greater the car's speed, the greater the thinking distance.

Breaking distance

Stopping distance is the sum of the thinking distance and the braking distance, i.e. it is the distance travelled by the car between the time the danger ahead is first detected and the time the car comes to a stop.

Stopping distance

1

State the difference between thinking distance and braking distance.

Thinking distance comes before braking distance. Thinking distance is the distance the car travels between the time the danger is detected and the brakes are applied, whereas the braking distance is the distance travelled after the brakes are applied until it comes to a stop.

Thinking distance is distance travelled between realisation and applying brakes.
Braking distance is distance travelled between applying brakes and vehicle stopping.

State the difference between thinking distance and braking distance.

2

Is the thinking distance between the position of when brakes are applied and a vehicle is stopped? Explain your answer.

Thinking distance is a distance between the position of when a danger is detected and brakes are applied.

No, it is a distance between danger detection and brakes being applied.

Is the thinking distance between the position of when brakes are applied and a vehicle is stopped? Explain your answer.

3

Given that a car's stopping distance is 42 m and the braking distance is 28 m, calculate the thinking distance of the car.

stopping distance = thinking + braking distance
thinking distance = 42 m โˆ’ 28 m = 14 m

14 m

Given that a car's stopping distance is 42 m and the braking distance is 28 m, calculate the thinking distance of the car.

4

Two identical cars travelling on the same road have the same thinking distance but the first car has a greater stopping distance than the second. Suggest a possible explanation to why this is.

Stopping distance = thinking + braking distance. Since the two cars have the same thinking distance, the difference in their stopping distances arises from a difference in their braking distances. The first car has a greater stopping distance and thus a greater braking distance. Since the two cars are being driven on the same road, this cannot be due to road conditions. Therefore, possible explanations are that the first car has poor tyre or brake conditions or the mass of the passengers of the first car is greater than that of the second car.

The first car has greater mass.

Two identical cars travelling on the same road have the same thinking distance but the first car has a greater stopping distance than the second. Suggest a possible explanation to why this is.

5

Explain how it is possible for two identical cars travelling on the same road to have the same braking distance, but the first car to have a greater stopping distance than the second.

Stopping distance = thinking + braking distance. Since the two cars have the same braking distance, the difference in their stopping distances arises from a difference in their thinking distances. Since the first car has a greater stopping distance, for a fixed braking distance it has a greater thinking distance. A possible explanation for this may be the fact that the driver is tired, distracted or under the influence of alcohol or drugs.

The driver of the first car is tired.

Explain how it is possible for two identical cars travelling on the same road to have the same braking distance, but the first car to have a greater stopping distance than the second.

End of page

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