Work done and energy transfer

Very long trains can be pulled by more than one engine.

A train is made up of four engines pulling trucks filled with coal.

The coal in one truck has a mass of 75 000 kg.

gravitational field strength = 9.8 N/kg

Calculate the weight of the coal in one truck.

Use the equation:

weight = mass × gravitational field strength

One engine exerts a forward force of 850 000 N.

Calculate the work done by one engine when the train moves a distance of 80 m.

Use the equation:

work done = force × distance moved

Each of the four engines exerts a forward force of 850 000 N on the trucks.

Calculate the total forward force on the trucks.

The force exerted by the engines on the trucks is a contact force.

Which of the following is also a contact force?

Tick (✓) one box.

Which sketch graph represents the train moving at a constant speed?

Tick (✓) one box.

The train accelerates for 150 s.

The velocity of the train changes from 16 m/s to 25 m/s.

Calculate the acceleration of the train.

Use the equation:

Figure 17 shows a young child using a baby walker.

The child is standing still.

What is the resultant vertical force on the child?

Give a reason for your answer.

Use the Physics Equations Sheet to answer questions 09.2 and 09.3.

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

The child pushed the baby walker 2.8 m across a horizontal floor.

The work done by the child was 35 J.

Calculate the horizontal force the child applied to the baby walker.

The child pushed the baby walker from a carpet onto a hard floor.

The child applied the same horizontal force to the baby walker.

Explain why the speed of the baby walker increased.

There are some toy gears on the front of the baby walker.

Figure 18 shows the gears.

The child applies a force to gear A.

This causes a moment about the pivot, so gear A rotates.

Use the Physics Equations Sheet to answer questions 09.5 and 09.6.

Write down the equation which links distance (d), force (F) and moment of a force (M).

The child applies a force of 2.0 N on gear A.

The perpendicular distance between the force and the pivot is 7.5 cm.

Calculate the moment of the force about the pivot.

Explain what happens to gear B when the child applies the force to gear A.

Figure 5 shows a young child using a baby walker.

The child is standing still.

What is the resultant vertical force on the child?

Give a reason for your answer.

Use the Physics Equations Sheet to answer questions 02.2 and 02.3.

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

The child pushed the baby walker 2.8 m across a horizontal floor.

The work done by the child was 35 J.

Calculate the horizontal force the child applied to the baby walker.

The child pushed the baby walker from a carpet onto a hard floor.

The child applied the same horizontal force to the baby walker.

Explain why the speed of the baby walker increased.

There are some toy gears on the front of the baby walker.

Figure 6 shows the gears.

The child applies a force to gear A.

This causes a moment about the pivot, so gear A rotates.

Use the Physics Equations Sheet to answer questions 02.5 and 02.6.

Write down the equation which links distance (d), force (F) and moment of a force (M).

The child applies a force of 2.0 N on gear A.

The perpendicular distance between the force and the pivot is 7.5 cm.

Calculate the moment of the force about the pivot.

Explain what happens to gear B when the child applies the force to gear A.

Figure 15 shows an electric super-car.

The battery in an electric car needs to be recharged.

Suggest two factors that affect the distance an electric car can travel before the battery needs to be recharged.

Use the Physics Equations Sheet to answer questions 08.2 and 08.3.

Write down the equation which links acceleration (a), change in velocity (Δ v) and time taken (t).

The maximum acceleration of the car is 20 m/s².

Calculate the time taken for the speed of the car to change from 0 m/s to 28 m/s at its maximum acceleration.

In a trial run, the car accelerates at 10 m/s² until it reaches its final velocity.

distance travelled by the car = 605 m

initial velocity of the car = 0 m/s

Calculate the final velocity of the car.

Use the Physics Equations Sheet.

Use the Physics Equations Sheet to answer questions 08.5 and 08.6.

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

When travelling at its maximum speed the air resistance acting on the car is 4000 N.

Calculate the work done against air resistance when the car travels a distance of 7.5 km at its maximum speed.

Figure 1 shows an electric super-car.

The battery in an electric car needs to be recharged.

Suggest two factors that affect the distance an electric car can travel before the battery needs to be recharged.

Use the Physics Equations Sheet to answer questions 01.2 and 01.3.

Write down the equation which links acceleration (a), change in velocity (Δ v) and time taken (t).

The maximum acceleration of the car is 20 m/s².

Calculate the time taken for the speed of the car to change from 0 m/s to 28 m/s at its maximum acceleration.

In a trial run, the car accelerates at 10 m/s² until it reaches its final velocity.

distance travelled by the car = 605 m

initial velocity of the car = 0 m/s

Calculate the final velocity of the car.

Use the Physics Equations Sheet.

Use the Physics Equations Sheet to answer questions 01.5 and 01.6.

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

When travelling at its maximum speed the air resistance acting on the car is 4000 N.

Calculate the work done against air resistance when the car travels a distance of 7.5 km at its maximum speed.

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.

A student investigated how the angle of a ramp affects the force required to hold a trolley stationary on the ramp. Figure 10 shows the equipment used.

Measure the angle Y in Figure 10

Figure 11 shows the newtonmeter before the investigation started.

What type of error is shown on the newtonmeter in Figure 11 ? Tick (✓) one box.

How can this error be corrected after the measurements have been taken? Tick (✓) one box.

Table 2 shows the corrected results.

Figure 12 is an incomplete graph of the results

Plot the missing results from Table 2 on Figure 12.

Figure 13 shows a person in a wheelchair using two different ramps to enter a van.

The ramps are at different angles to the ground. Explain one advantage of using the long ramp compared with using the short ramp.

A force of 160 N is used to move the wheelchair up the long ramp. The ramp is 2.5 m long. Calculate the work done to move the wheelchair up the ramp. Use the equation: work done = force × distance

An aircraft travels at a constant velocity. How is the velocity of the aircraft different to the speed of the aircraft?

Figure 11 shows one of the engines on the aircraft.

Air is taken into the front of the engine and pushed out of the back of the engine. Explain the effect this has on the engine.

Figure 12 shows a distance-time graph for the aircraft.

Determine the speed of the aircraft.

Write down the equation that links acceleration (a), change in velocity (Δ v) and time taken (t).

At a different stage of the flight, the aircraft was travelling at a velocity of 250 m/s. The aircraft then decelerated at 0.14 m/s². Calculate the time taken for the aircraft to decelerate from 250 m/s to 68 m/s.

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

When the aircraft landed, it travelled 2000 m before stopping. The work done to stop the aircraft was 140 000 000 J. Calculate the mean force used to stop the aircraft.

Mean force = N

Figure 8 shows a student playing with a remote-controlled car.

The remote control transmits radio waves to the car aerial. The transmitted radio waves have a frequency of 320 MHz. speed of radio waves = 3.0 10⁸ m/s Calculate the wavelength of the radio waves. Give the unit.

The car aerial is connected to an electrical circuit in the car. Describe what happens in the electrical circuit when the car aerial absorbs radio waves.

The car produces sound waves. Give two ways in which radio waves are different to sound waves.

Figure 9 shows the distance-time graph for the first 30 seconds of the car’s motion.

Describe the motion of the car during the first 30 seconds.

Determine the speed of the car 20 seconds after it started to move.

A different car accelerated from 0.12 m/s to 0.52 m/s. The acceleration of the car was 0.040 m/s². The work done to accelerate the car was 0.48 J. Calculate the resultant force needed to accelerate the car.

Explain why the car has a maximum speed.

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.

Figure 9 shows a fork-lift truck lifting a heavy crate.

The crate weighs 11 500 N and is lifted vertically 2.60 m. Calculate the work done to lift the crate. Use the equation: work done = force × distance

The weight of the crate causes a clockwise moment of 13 800 Nm about the centre of the front wheel of the fork-lift truck.

The weight of the fork-lift truck and driver cause an anticlockwise moment. What is the minimum size of the anticlockwise moment needed so that the fork-lift truck does not topple over?

Write down the equation which links distance, force and moment of a force.

Calculate the distance ‘ d ’ marked on Figure 9.

A child drops a ball. The ball hits the ground and bounces. Figure 1 shows the velocity-time graph for the ball from when the ball is dropped until when the ball reaches the top of its first bounce. Air resistance has been ignored.

Describe the motion of the ball between points A and B on Figure 1.

What direction is the ball moving between points C and D on Figure 1 ?

The ball and the Earth form a system. What is meant by ‘a system’? Tick one box.

When the ball hits the ground, energy is transferred from the ball to the Earth. Explain how the data in Figure 1 shows this energy transfer.