Forces & braking

The stopping distance of a car is affected by the condition of the brakes and tyres.

A car is being driven around a corner when the driver sees some roadworks.

The driver applies the brakes when the car is 24 m away from the roadworks.

The velocity of the car changes from 18 m/s to 0 m/s.

Calculate the constant deceleration needed to stop the car in a distance of 24 m.

Use the Physics Equations Sheet.

As a safety measure, the speed limit on the road was reduced.

Explain how the safety of road users is affected by:

• the condition of the brakes and tyres

• reduced speed.

You should refer to thinking distance and braking distance.

Two identical cars were driven along a straight, level road.

One car had a greater speed than the other car.

The driver of each car applied the brakes until the cars stopped.

Both cars travelled the same distance while braking.

Explain how braking from a greater speed affected the risk of the brakes overheating.

The stopping distance of a car is affected by the condition of the brakes and tyres.

A car is being driven around a corner when the driver sees some roadworks.

The driver applies the brakes when the car is 24 m away from the roadworks.

The velocity of the car changes from 18 m/s to 0 m/s.

Calculate the constant deceleration needed to stop the car in a distance of 24 m.

Use the Physics Equations Sheet.

As a safety measure, the speed limit on the road was reduced.

Explain how the safety of road users is affected by:

• the condition of the brakes and tyres

• reduced speed.

You should refer to thinking distance and braking distance.

Two identical cars were driven along a straight, level road.

One car had a greater speed than the other car.

The driver of each car applied the brakes until the cars stopped.

Both cars travelled the same distance while braking.

Explain how braking from a greater speed affected the risk of the brakes overheating.

The stopping distance of a car depends on the thinking distance and the braking distance.

Which of the following affects the thinking distance?

Tick () one box.

A car manufacturer tested three different types of tyre which were fitted to three identical cars.

This is the method used.

1. Drive the car along a road.

2. Apply the brakes until the car stops.

3. Measure the distance travelled while braking.

4. Repeat steps 1 to 3 for each car when the road is dry and when the road

is wet.

The brakes were applied with the same force for each test.

Give one other variable that should have been kept the same for each test.

Figure 10 shows the results.

The manufacturer wants to put the safest tyres on a new car.

Evaluate the safety of each type of tyre.

Use data from Figure 10.

When the brakes are applied, a force does work to stop the car.

Use the Physics Equations Sheet to answer questions 05.4 and 05.5.

Write down the equation that links distance (s), force (F) and work done (W).

The braking force acting on a car is 6000 N.

The work done to stop the car is 300 000 J.

Calculate the braking distance of the car.

Explain how the force applied by the brakes affects the braking distance of the car.

A safety test was carried out to determine how the speed of a car affects the stopping distance of the car.

At the start of the test the car was moving slowly.

Then the car accelerated at 5.8 m/s² for 2.5 s.

The final velocity of the car was 20 m/s.

Calculate the initial velocity of the car.

Use the Physics Equations Sheet.

The reaction time of the driver was measured.

How can the reaction time of the driver be used to calculate the thinking distance?

The car was driven at a constant speed. The driver applied the maximum braking force, and the braking distance was measured.

The test was repeated at different speeds.

Figure 8 shows the results.

Which of the following gives the relationship between the speed and the braking distance?

Tick () one box.

During one test the brakes were applied with a force of 6250 N.

The deceleration of the car was 5.0 m/s².

The braking distance of the car was 14.4 m.

Determine the momentum of the car before the brakes were applied.

Use the Physics Equations Sheet.

Use Figure 8.

Momentum = kg m/s

A car contains a device called a black box. The black box records the distance travelled and the time taken for each journey. Figure 3 shows the distance–time graph for part of a journey.

Which feature of Figure 3 shows that the car travels at a constant speed for the first 4 seconds? Tick (✓) one box.

After 4 seconds the driver applied the brakes and the car slowed down and stopped. The distance the car travelled after the brakes were applied is called the braking distance. Determine the braking distance of the car. Use Figure 3.

The black box also records the deceleration of the car.

As the car decelerates, the velocity of the car changes by 16 m/s. The car decelerates for 2.5 seconds. Calculate the deceleration of the car. Use the equation:

If the black box records large decelerations, it identifies that the driving may be dangerous. Why can large decelerations be dangerous? Tick (✓) two boxes.

The black box monitors the speed of the car. Describe how speed affects braking distance.

A car contains a device called a black box. The black box records the velocity and acceleration of the car. The car was travelling at a constant velocity. The driver then reacted to a hazard. Figure 11 shows the velocity–time graph for the car.

Determine the deceleration of the car. Give the unit.

The driver of the car has a reaction time of 0.75 s. Determine the stopping distance of the car. Use the Physics Equations Sheet. Use Figure 11.

If the black box records large decelerations, it identifies that the driving may be dangerous. Explain why large decelerations may be dangerous.

The stopping distance of a car is the sum of the thinking distance and the braking distance.

Which factors affect the thinking distance? Tick (✓) two boxes.

Explain why a person should not drink alcohol and then drive.

The Highway Code gives information on how thinking distance depends on the speed

of a car. Figure 7 shows the information as a graph.

What is the speed of a car if the thinking distance is 16 m?

Describe the relationship between speed and thinking distance.

The Highway Code assumes the driver’s reaction time is 0.70 seconds. Draw a line on Figure 7 to show the relationship for a driver with a reaction time of 1.4 seconds.

A car accelerates at 5.0 m/s² over a distance of 45 m initial velocity of the car = 0 m/s Calculate the final velocity of the car. Use the Physics Equations Sheet. Give your answer to 2 significant figures.

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.

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

Figure 10 shows how the velocity of a car changes during braking.

Determine the braking distance of the car.

Explain how the gradient of the line on Figure 10 shows that the resultant force on the car was not constant.

The stopping distance of a car is the sum of the thinking distance and the braking distance.

The thinking distance is affected by the reaction time of the driver.

Which two of the following can affect the reaction time of the driver?

Tick (✓) two boxes.

Scientists measured the reaction time for drivers of different ages.

Figure 6 shows the results.

At what age did the drivers have the lowest mean reaction time?

What was the lowest mean reaction time?

The braking distance of a car is the distance travelled between the driver applying the

brakes and the car stopping.

Complete the sentences.

Choose answers from the box.

Each answer may be used once, more than once or not at all.

When the brakes are applied, the kinetic energy of the

car.

The temperature of the brakes.

A car is travelling at a speed of 12 m/s.

The driver applies the brakes and the car decelerates at a constant 3.0 m/s².

Calculate the braking distance of the car.

Use the equation:

Choose the unit from the box.

To pass the UK driving test, people must know the typical stopping distance of a car at certain speeds.

Suggest one reason why.

The speed limit on many roads in towns is 13.5 m/s Outside schools this speed limit is often reduced by one-third.

Calculate the reduced speed limit.

A reduced speed limit may reduce air pollution. Explain one other advantage of a reduced speed limit.

Figure 11 shows a car being driven at a constant speed past a speed camera.

The camera recorded two images of the car 0.70 s apart. The car travelled 14 m between the two images being taken. The maximum deceleration of the car is 6.25 m/s² Calculate the minimum braking distance for the car at the speed it passed the speed camera.

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.

The thinking distance of a car depends on the reaction time of the driver.

Figure 6 shows how thinking distance varies with reaction time for a car travelling at 30 m/s

The reaction time of a driver can double if the driver is distracted.

Explain the effect doubling the reaction time has on the thinking distance.

Use data from Figure 6.

Give the reason why there are no values of thinking distance for reaction times less than 200 milliseconds.

A driver measured her reaction time using an online test. She did the test five times.

Table 2 shows the results.

How does the data in Table 2 show that it was important that the driver did the test five times?

Calculate the mean reaction time of the driver.

The driver is driving her car at 30 m/s

Determine the thinking distance.

Use Figure 6 and your answer from Question 04.4

The driver applies the brakes and the car comes to a stop.

The force exerted by the brakes affects the braking distance.

Give two other factors that affect the braking distance.

Write down the equation that links distance, force and work done.

When the driver applies the brakes, there is a constant resultant force of 6.0 kN on the car.

The car travels a distance of 75 m before stopping.

Calculate the work done in stopping the car.

Figure 10 shows a lorry.

The brakes of the lorry are in a poor condition.

What effect will the condition of the brakes have on thinking distance and the braking distance of the lorry?

Thinking distance

Using a hand-held mobile phone while driving is illegal in the United Kingdom.

Table 1 shows the effect of using a mobile phone on thinking distance.

Explain why driving while using a hand-held mobile phone is more dangerous than using a mobile phone with a hands-free kit.

Use data from Table 1

Figure 8 shows the distance-time graph for a car travelling at 15 m/s

When the driver is tired, his reaction time increases from 0.50 seconds to 0.82 seconds. Determine the extra distance the car would travel before the driver starts braking.

When the brakes are used, the temperature of the brakes increases. Explain why. Use ideas about energy in your explanation.

A lorry travels 84 m with a constant acceleration of 2.0 m/s² to reach a velocity of 19 m/s Calculate the initial velocity of the lorry. Use the Physics Equations Sheet.

Figure 9 shows how the thinking distance, braking distance and stopping distance for a car vary with the speed of the car.

Describe the relationships shown in Figure 9 You should include factors that would affect the gradient of the lines.