Energy stores and systems

Figure 8 shows apparatus set up to investigate the speed of a falling object.

The object is dropped from rest at the position shown. The object falls through the light gate.

The speed of the object, after it has fallen through a height, h, is measured by the light gate.

Label Figure 8 to show the height, h. Your label should look like this

The speed is measured at least four times for each drop height.

Give one reason for repeating the measurements.

The metre rule shown in Figure 8 is used to measure the height, h.

Suggest two ways to make the measurement of h as accurate as possible.

As the object in Figure 8 falls, energy is transferred.

These energy transfers are represented in Figure 9.

Complete the labels of the energy stores involved.

Figure 10 shows wind power generation from the year 2000 onwards.

Estimate the percentage change in wind power generation from 2005 to 2020.

percentage change =_........

Figure 18 shows a person on a skateboard at the top of a ramp.

At P, the person is not moving.

The person rides the skateboard down the ramp from P to Q.

The gravitational potential energy of the person decreases by 980 J.

The mass of the person is 35 kg.

Calculate h, the height of the ramp.

Use g = 10 N/kg.

Use the equation

change in gravitational potential energy = m g h

The kinetic energy, KE, of the person at Q is 950 J.

The mass of the person is 35 kg.

Calculate the velocity of the person at Q.

Use the equation

Figure 19 is a diagram that represents energy changes from P to Q.

State what is represented by X.

Calculate the value of X.

Calculate the efficiency of the system represented in Figure 19.

The person would like to start from P again but have a greater velocity at Q.

Suggest two ways that this can be achieved.

Figure 2 shows a person on a skateboard at the top of a ramp.

At P, the person is not moving.

The person rides the skateboard down the ramp from P to Q.

The gravitational potential energy of the person decreases by 980 J.

The mass of the person is 35 kg.

Calculate h, the height of the ramp.

Use g = 10 N/kg.

Use the equation

change in gravitational potential energy = m g h

The kinetic energy, KE, of the person at Q is 950 J.

The mass of the person is 35 kg.

Calculate the velocity of the person at Q.

Use the equation

Figure 3 is a diagram that represents energy changes from P to Q.

State what is represented by X.

Calculate the value of X.

Calculate the efficiency of the system represented in Figure 3.

Figure 11 shows a truck on a horizontal road.

A force of 1200 N pulls the truck along the road for a distance of 8.0 m.

Calculate the work done by the 1200 N force.

Use the equation

work done = force distance moved in the direction of the force

State the unit of work done.

work done =_........

At 8.0 m the force is removed and the truck slows down until it stops.

Describe the energy transfers as the truck slows down.

A box has a mass of 90 kg.

Which of these is the weight of the box?

Figure 12 shows a truck lifting a different box.

A student calculates the change in gravitational potential energy, ΔGPE, for the box at different heights.

Figure 13 shows the results of the student’s calculations.

The student has made one incorrect calculation.

The truck lifts the box from the ground to a height of 2.0 m.

This takes a time of 5.0 s.

Using data from the graph in Figure 13, calculate the power needed to lift the box.

Use the equation

power =_........

Figure 17 shows a football kicked against a wall.

The football has a mass of 0.42 kg.

The football gains 11 J of gravitational potential energy as it moves from the ground to the wall.

Calculate the height at which the ball hits the wall.

Gravitational field strength = 10 N / kg

Use the equation

∆ GPE = m × g × ∆ h

Calculate the kinetic energy of the football when it is moving at a velocity of 12 m / s.

Use the equation

Describe the energy transfers that happen when the ball hits the wall.

*(b) In the UK, electricity is generated using non‑renewable and renewable energy resources.

The graph in Figure 18 shows how the amount of electricity generated by these resources changed from 2012 to 2020.

30

25

20

time in years from 2012 to 2020

Figure 18

Explain how and why the amount of electricity generated by renewable and non-renewable energy resources has changed from 2012 to 2020.

Your answer should include

• the trends shown in Figure 18

• the change in the amount of electricity generated by at least one renewable resource

• the change in the amount of electricity generated by at least one non‑renewable resource.

Figure 5 shows a football kicked against a wall.

The football has a mass of 0.42 kg.

The football gains 11 J of gravitational potential energy as it moves from the ground to the wall.

Calculate the height at which the ball hits the wall.

Gravitational field strength = 10 N / kg

Use the equation

∆ GPE = m × g × ∆ h

Calculate the kinetic energy of the football when it is moving at a velocity of 12 m / s.

Use the equation

Describe the energy transfers that happen when the ball hits the wall.

A stone is held at rest above the ground.

The stone is released and falls until its velocity is 17 m / s.

Calculate the distance the stone has fallen when its velocity has reached 17 m / s.

Which statement describes conservation of energy in a closed system?

A student uses the apparatus in Figure 12 to find out which of two materials, sand or sawdust, is the better insulator.

The student also has a kettle to boil water, a thermometer and a stop clock.

Draw a labelled diagram to show how the student should set up the equipment to investigate which material is the better insulator.

Give three factors that the student must control in this investigation.

Expanded polystyrene, used to insulate buildings, has different densities.

Figure 13 shows how the thermal conductivity of expanded polystyrene changes with the density of expanded polystyrene.

density of expanded polystyrene in kg/m³

Figure 13

Using the graph in Figure 13, describe how the thermal conductivity of expanded polystyrene changes with the density of expanded polystyrene.

Figure 14 is an energy diagram for an electric kettle, used to heat water.

one second = 3000 J one second

one second = 2400 J

Calculate the amount of energy lost to the surroundings in one second.

energy lost to the surroundings in one second =_........

Calculate the efficiency of the kettle.

Use the equation

An aircraft starts from rest and accelerates along the runway for 36 s to reach take‑off velocity.

Take‑off velocity for this aircraft is 82 m/s.

Show that the acceleration of the aircraft along the runway is about 2 m/s².

Assume the acceleration is constant.

Calculate the distance the aircraft travels along the runway before take‑off.

Use the equation

Suggest one reason why the length of the runway used is always much longer than the calculated distance that the aircraft travels along the runway before take-off.

The aircraft lands with a velocity of 71 m/s.

Calculate the kinetic energy of the aircraft as it lands.

When the aircraft has come to a stop, all the kinetic energy has been transferred to the surroundings.

Give one way that the energy has been transferred to the surroundings.

Figure 15 shows a ‘Mars rover’ descending to the surface of the planet Mars.

Calculate the change in gravitational potential energy of the rover as it descends from position P to position Q.

Mass of rover = 1100 kg

Gravitational field strength on Mars = 3.7 N / kg

Give your answer to 2 significant figures.

change in gravitational potential energy =_........

Use data from Figure 15 to calculate the change in kinetic energy of the rover as it descends from position P to position Q.

change in kinetic energy =_........

The rover is slowed down safely using thrusters and a parachute (not shown in Figure 15).

The thrusters use jets of gas to control movements and the parachute is designed to be used in the atmosphere of Mars.

Describe the energy changes involved in terms of the work done by various forces as the rover descends.

The rover uses solar panels for its power needs.

The solar panels can provide 1200 W of power.

Show that the solar panels can provide 2.16 MJ of energy in 30 minutes.

The solar panels convert 27% of the energy they receive from the Sun into electricity.

Calculate the solar energy received by the panels that provides the 2.16 MJ of energy.

energy received =_........

A cyclist has a mass of 64 kg.

The cyclist rides from a flat road to the top of a hill.

The top of the hill is 24 m above the flat road.

Calculate the gain in gravitational potential energy, ∆ GPE, of the cyclist.

Use g = 10 N/kg

Use the equation

The cyclist returns to the flat road.

The mass of the cyclist is 64 kg.

Calculate the kinetic energy of the cyclist when the cyclist is travelling at 6.0 m/s.

Use the equation

The cyclist then uses the brakes on the bicycle to stop.

Explain what happens to the kinetic energy of the cyclist.

A different cyclist uses a motorised bicycle.

The motorised bicycle is powered by an electric motor.

Figure 3 is an energy diagram for the motor.

Calculate how much energy is wasted.

Calculate the efficiency of the electric motor.

Use the equation:

A student lifts a toy car from a bench and places the toy car at the top of a slope as shown in Figure 16.

Describe an energy transfer that occurs when the student lifts the toy car from the bench and places the toy car at the top of the slope.

The student lets the toy car roll down the slope.

Describe how the student could find, by experiment, the speed of the toy car at the bottom of the slope.

The student needs to develop the experiment to determine the loss in potential energy and the gain in kinetic energy as the toy car is rolling down the slope.

State the other measurements the student must make.

When the toy car rolls down the slope, some energy is transferred to the surroundings as thermal energy.

State how the student could calculate the amount of energy transferred to the surroundings.

Explain one way the student could reduce the amount of thermal energy transferred to the surroundings as the toy car rolls down the slope.

Figure 10 shows a toy used to launch a ball.

One end of the spring is fixed to the handle.

The other end of the spring is fixed to the support.

A child pulls the handle, stretching the spring.

Figure 11 shows the toy with the spring stretched.

Which of these shows the forces acting on the handle when the child keeps the spring stretched?

Ignore the force due to gravity.

In Figure 11, the extension of the spring is 0.070 m.

The spring constant (k) is 20 N/m.

Calculate the force used to extend the spring.

Use the equation

The child pulls the handle until the pad is against the support as shown in Figure 12.

The extension of the spring is 0.09 m.

The spring constant (k) is 20 N/m.

Calculate the work done in extending the spring by 0.09 m.

Use the equation

work done = ½ k(extension)²

The child lets go of the handle.

The ball starts to move.

The spring returns to its original length.

Describe the energy transfer that takes place when the ball starts to move.

The child can only stretch the spring until the pad is pressing against the support.

Explain how the design of the toy prevents the spring from becoming damaged.

Figure 23 shows a drone.

The drone has four spinning blades.

The upward force produced enables the drone to rise in the air.

The speed at which the blades spin is measured in turns per minute.

Figure 24 shows how the upward force produced by the four blades depends on the speed at which the blades spin.

Describe the relationship between upward force and speed shown by this graph.

A different drone has a mass of 4.5 kg.

This drone rises from the ground to a height of 20 m.

Calculate the change in gravitational potential energy when the drone rises through a height of 20 m.

The gravitational field strength g = 10 N/kg.

State the amount of useful work done by the blades as the drone rises through 20 m.

It takes 4 s for the drone to rise through 20 m.

Calculate the useful power developed by the blades in this time of 4 s.

*(c) The blades on the drone are turned by electric motors.

The electric motors are powered by a battery.

Figure 25 represents the energy transfers involved when the drone rises from the ground.

Describe the changes in the way energy is stored when the drone rises from the ground.

Your answer should refer to energy transfers.

Figure 5 shows a way of projecting a small trolley up a sloping track.

When the button is pressed, a spring is released in P that projects the trolley up the track.

The trolley travels up the track, stops and then rolls back down.

The spring in P always exerts the same force when projecting the trolley.

A student investigates how the mass of the trolley affects the maximum vertical height, h, reached by the trolley.

State the measurements the student should make to complete the investigation.

You should make use of the equipment shown in Figure 5 and any other equipment that is needed.

Figure 6 is a graph of the student’s results.

The student states that the energy transferred by the spring is the same each time it is used.

Use data from any two points on the graph in Figure 6 to support this statement.

Describe how the student could extend the investigation to determine the average speed of the trolley as it rolls back down the track.

Figure 6 shows a spinning flywheel.

State how energy is stored in a spinning flywheel.

State one way to increase the amount of energy stored in the flywheel.

Figure 7 shows a skier going down a hill.

She descends through a vertical height of 200 m.

The skier’s mass is 65 kg.

Calculate the change in gravitational potential energy.

Use the equation

Δ GPE = m × g × Δ h

Take the gravitational field strength, g, as 10 N / kg.

At the bottom of the slope her speed was 36 m/s.

Calculate her kinetic energy at the bottom of the slope.

Use the equation

Describe how her speed at the bottom of the slope could be determined.