Forces and braking

Car X and car Y have engines that produce the same maximum forward force.

The cars are the same shape, but car X has a greater mass than car Y.

How does the maximum acceleration of car X and car Y compare?

Tick (✓) one box.

Car Y has a mass of 900 kg.

Calculate the resultant force on car Y.

Use the equation:

resultant force = mass × acceleration

A car moves at a constant speed on a level road.

Figure 4 shows the horizontal forces on the car.

The driver makes the car accelerate until the car reaches its maximum speed.

Explain how the horizontal forces on the car change as the car accelerates to its maximum speed.

To pass a driving test, drivers need to understand the difference between thinking distance and braking distance.

Complete the sentence.

Choose the answer from the box.

Complete the sentence.

Choose the answer from the box.

The braking distance is the distance travelled by the car under the braking

Figure 5 shows how speed affects the thinking distance and braking distance of a car.

The car is moving at a speed of 100 km/h.

Calculate the stopping distance of the car.

Use Figure 5.

Which two of the following would increase the stopping distance of a car?

Tick (✓) two boxes.

A car manufacturer makes two cars, X and Y.

The cars are identical, apart from their mass.

Car X has a greater mass than car Y.

How does the maximum acceleration of car X compare with the maximum acceleration of car Y ?

Cars have air bags that inflate to protect the driver if the car stops very suddenly.

Explain how air bags reduce the chance of injury to the driver.

Car X has a mass of 1400 kg and is travelling at 18 m/s.

The driver applies the brakes.

The car has a constant deceleration and comes to a stop in a distance of 24 m.

Calculate the resultant force on the car.

Use the Physics Equations Sheet.

Explain why braking causes an increase in the temperature of the brakes.

The driver of a car applies the brakes so the car has a large deceleration.

Give two possible risks of a large deceleration.

Figure 12 shows a velocity–time graph for a train travelling between two stations.

Determine the distance travelled by the train in the first 600 s of the journey.

Explain what happens to the braking force as the train decelerates.

Use information from Figure 12.

Determine the maximum deceleration of the train.

Another train travels at a speed of 60 m/s.

A constant braking force of 270 000 N causes the train to decelerate and stop.

mass of train = 240 000 kg

Calculate the distance travelled while the braking force is applied.

Use the Physics Equations Sheet.

It is illegal for train drivers to drink alcohol before driving a train.

Explain how drinking alcohol would affect the stopping distance of a train.

The stopping distance of a car is the braking distance added to the thinking distance.

Complete the sentences. Choose answers from the box.

A driver applies the brakes to a moving car.

energy of the car.

energy store of the brakes.

Figure 3 shows how the speed of the car affects the minimum braking distance of the car.

Describe the relationship between the speed of the car and the minimum braking distance of the car.

Complete the sentence. Choose the answer from the box.

A car driver applies the brakes to decelerate the car as it approaches a road junction. The car decelerates at 0.25 m/s². mass of the car = 1600 kg

Calculate the time taken for the velocity of the car to decrease from 12.5 m/s to 5.0 m/s. Use the equation:

Calculate the resultant force causing the car to decelerate. Use the equation: resultant force = mass × deceleration

Thinking distance is affected by the reaction time of the driver. Figure 4 shows how a student tested a person’s reaction time.

The student held a ruler and then released it. The person being tested closed his hand to catch the ruler as quickly as possible. The further the ruler fell the greater the person’s reaction time.

The student wanted to test the reaction time of the people in her class. Which of the following could have been a control variable in this investigation? Tick (✓) one box.

The student tested three people in her class. The mean distance that the ruler fell before being caught was 18.2 cm. If all of the people in her class were tested, the mean distance may not be 18.2 cm. Suggest why.

Describe how this investigation could be changed to find out how listening to music affects reaction time.

Some cars have a lever that is used to apply the handbrake. Figure 8 shows the handbrake lever in a car.

The driver applies the force shown in Figure 8. The force produces a moment about the pivot. How could the driver increase the moment about the pivot without increasing the size of the force?

The driver releases the handbrake. Figure 9 shows how the velocity of the car changes during the first 5 seconds of a journey.

After 3 seconds, the momentum of the car is 24 000 kg m/s. Calculate the mass of the car. Use the Physics Equations Sheet.

Determine the distance travelled by the car during the first 5 seconds of the journey. Use Figure 9.

In an emergency the driver needs to apply the brakes suddenly to stop the car quickly. The driver of the car is distracted. Explain why the distraction will increase the stopping distance.

Explain why the temperature of the brakes increases as they are used.

Speed limits on roads increase safety.

The braking distance of a car increases as the speed of the car increases.

Give two other factors that increase the braking distance of a car.

Explain why the driver’s reaction time affects the thinking distance of a car.

Scientists have investigated how drinking alcohol affects a person’s reaction time.

Figure 5 shows the results of the investigation.

Which of the following conclusions can be made using Figure 5 ?

Tick (✓) two boxes.

Figure 6 shows some speed cameras on a road.

The speed cameras determine the average speed of cars on the road.

The speed limit on the road in Figure 6 is 20 m/s.

The cameras in Figure 6 are 1.5 km apart.

Calculate the minimum time it takes to travel 1.5 km without breaking the speed limit.

Use the Physics Equations Sheet.

The average speed of a car between the cameras and the average velocity of the car between the cameras are different.

Explain why.

The thinking distance and braking distance for a car vary with the speed of the car.

Explain the effect of two other factors on the braking distance of a car. Do not refer to speed in your answer.

Which equation links acceleration (a), mass (m) and resultant force (F). Tick (✓) one box.

The mean braking force on a car is 7200 N. The car has a mass of 1600 kg. Calculate the deceleration of the car.

Figure 18 shows how the thinking distance and braking distance for a car vary with the speed of the car.

Determine the stopping distance when the car is travelling at 80 km/h.

Figure 19 shows part of the braking system for a car.

Which equation links area of a surface (A), the force normal to that surface (F) and pressure (p)? Tick (✓) one box.

When the brake pedal is pressed, a force of 60 N is applied to the piston. The pressure in the brake fluid is 120 000 Pa. Calculate the surface area of the piston. Give your answer in standard form. Give the unit.

The thinking distance and braking distance for a car vary with the speed of the car.

Explain the effect of two other factors on the braking distance of a car. Do not refer to speed in your answer.

Which equation links acceleration (a), mass (m) and resultant force (F). Tick (✓) one box.

The mean braking force on a car is 7200 N. The car has a mass of 1600 kg. Calculate the deceleration of the car.

Figure 1 shows how the thinking distance and braking distance for a car vary with the speed of the car.

Determine the stopping distance when the car is travelling at 80 km/h.

Figure 2 shows part of the braking system for a car.

Which equation links area of a surface (A), the force normal to that surface (F) and pressure (p). Tick (✓) one box.

When the brake pedal is pressed, a force of 60 N is applied to the piston. The pressure in the brake fluid is 120 000 Pa. Calculate the surface area of the piston. Give your answer in standard form. Give the unit.

The driver of a vehicle sees a hazard on the road. The driver uses the brakes to stop the vehicle. Explain the factors that affect the distance needed to stop a vehicle in an emergency.

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

The work done by the braking force to stop a vehicle was 900 000 J The braking force was 60 000 N

Calculate the braking distance of the vehicle.

The greater the braking force, the greater the deceleration of a vehicle. Explain the possible dangers caused by a vehicle having a large deceleration when it is braking.

The driver of a vehicle sees a hazard on the road. The driver uses the brakes to stop the vehicle. Explain the factors that affect the distance needed to stop a vehicle in an emergency.

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

The work done by the braking force to stop a vehicle was 900 000 J The braking force was 60 000 N

Calculate the braking distance of the vehicle.

The greater the braking force, the greater the deceleration of a vehicle. Explain the possible dangers caused by a vehicle having a large deceleration when it is braking.