Momentum

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.

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.

Figure 14 shows some bumper cars. Bumper cars are designed to withstand collisions at low speeds.

During a collision between a bumper car and the barrier, the bumper car and barrier act as a closed system. What is meant by a ‘closed system’?

How does Newton’s Third Law of motion apply to the collision between the bumper car and the barrier?

During the collision, the change in momentum of the bumper car is 700 kg m/s. The time taken for the collision is 0.28 s. Calculate the force on the bumper car during the collision. Use the Physics Equations Sheet.

The bumper car has a flexible bumper. Explain how the flexible bumper reduces the risk of injury to the people in the bumper car during the collision.

A bumper car moved with an initial constant velocity and then accelerated

While accelerating, the bumper car travelled a distance of 1.5 m. The final velocity of the bumper car was 2.5 m/s. Calculate the initial constant velocity of the bumper car. Use the Physics Equations Sheet.

Hailstones are small balls of ice. Hailstones form in clouds and fall to the ground.

Figure 7 shows different-sized hailstones.

A hailstone falls from a cloud and accelerates.

Why does the hailstone accelerate?

The hailstone stops accelerating and reaches terminal velocity.

Explain why the hailstone reaches terminal velocity.

A scientist investigated how the mass of hailstones affects their terminal velocity.

Figure 8 shows the results.

Why does terminal velocity increase with mass?

Tick (✓) one box.

Explain the difference in the maximum kinetic energy of a hailstone with a mass of 10 g and a hailstone with a mass of 20 g.

The kinetic energy of a hailstone is measured in joules.

Which of the following is the same as 1 joule?

Tick (✓) one box.

Figure 8 is repeated below.

A hailstone hit the ground at its terminal velocity of 25 m/s.

The hailstone took 0.060 s to stop moving.

Determine the average force on the hailstone as it hit the ground.

Use information from Figure 8.

Use the Physics Equations Sheet.

Figure 7 shows two ice hockey players moving towards each other. They collide and then move off together.

During the collision, the total momentum of the players is conserved.

What is meant by ‘momentum is conserved’?

Immediately after the collision the two players move together to the right. Calculate the velocity of the two players immediately after the collision.

The ice hockey players wear protective pads filled with foam. Explain how the protective pads help to reduce injury when the players collide.

An adult of mass 80 kg has more inertia than a child of mass 40 kg What is inertia?

A teacher demonstrated the idea of a safety surface. She dropped a raw egg into a box filled with pieces of soft foam. The egg did not break. Figure 10 shows the demonstration.

Explain why the egg is less likely to break when dropped onto soft foam rather than onto a concrete floor.

Figure 11 shows a child on a playground swing. The playground has a rubber safety surface.

A child of mass 32 kg jumped from the swing. When the child reached the ground she took 180 milliseconds to slow down and stop. During this time an average force of 800 N was exerted on her by the ground.

Calculate the velocity of the child when she first touched the ground. Use the Physics Equations Sheet.