Energy stores & systems

The diagrams show a spring hanging from a nail.

• diagram 1 shows the spring with no weight added

• diagram 2 shows the spring stationary, after a weight has been added

• diagram 3 shows the spring after the weight has been pulled down

weight

Diagram 1
Diagram 2
Diagram 3

Which energy store has increased for the spring in diagram 2 compared to the spring in diagram 1?

The spring is released from the position shown in diagram 3.

Describe the energy transfers that take place until the spring stops vibrating.

Shock absorbers containing springs are used on motorcycles. Shock absorbers are designed to compress and expand as the motorcycle moves across a rough surface.

A new type of shock absorber has been developed to generate electricity from the movement of the motorcycle.

This new type of shock absorber consists of magnets that slide inside a coil when the motorcycle goes over a bump.

Some of the energy that would normally be wasted can be recovered, so fuel is saved.

Which of these statements best describes the advantage of this new type of shock absorber?

Explain how this new type of shock absorber can generate electricity.

Road X has a rough surface.

Road Y has a smooth surface.

(Source: © MikhailSh / Shutterstock)
(Source: © BearFotos / Shutterstock)

Road X
Road Y

A motorcycle travels at the same speed along road X and road Y.

Explain why the new type of shock absorber will generate more electricity for this motorcycle on road X than on road Y.

The photograph shows a wind turbine used for supplying energy on a large scale.

Describe a change in the turbine’s energy stores from when the turbine is at rest to when it is moving at full speed.

Describe a change in the turbine’s energy stores when the wind is blowing but the turbine moves at constant speed.

State the formula linking efficiency to useful energy output and total energy output.

The wind transfers 1.2 × 10⁶J of energy to the turbine.

The total mass of the turbine blades is 16 000 kg.

The wind causes the turbine blades to accelerate from rest to an average speed of 7.6 m/s.

Calculate the efficiency of the turbine.

This question is about the evolution of a star.

A main sequence star is created in a collapsing region of a nebula.

The table gives different energy stores for the gases in the collapsing nebula, from when the nebula starts to collapse to just before the main sequence star is created.

Complete the table by placing ticks () to show whether each energy store increases, decreases or stays the same.

At the end of the main sequence stage of a star’s evolution, the star can become a red giant or a red supergiant.

Give the property of a star that determines whether it becomes a red giant or a red supergiant.

A red giant star eventually becomes a white dwarf star.

Discuss the differences between a red giant star and a white dwarf star.

A student stretches a rubber band.

The photographs show a rubber band before and after it has been stretched.

State which energy store increases in the rubber band after it has been stretched.

State the main method of energy transfer when the rubber band is stretched.

State the source of the energy transferred to the rubber band.

The diagram shows a force-extension graph for a rubber band.

State how the graph shows that the rubber band does not obey Hooke’s law.

Explain how the graph shows that the rubber band is elastic.

The student stretches the rubber band and then releases it. The band moves vertically upwards.

The band travels with an initial speed of 13 m / s.

When the band reaches its maximum height above the student’s hand, the band has a speed of 0 m / s.

Calculate the maximum height that the band reaches.

Give your answer to 2 significant figures.

[acceleration due to gravity = −10 m / s²]

The band reaches its maximum height.

Explain the motion of the band as it falls from its maximum height to the ground.

Refer to forces in your answer.

You may assume

• the band does not rotate

• the band does not reach terminal velocity

A hydroelectric power (HEP) station generates electricity from renewable energy resources.

State what is meant by the term renewable energy resource.

The diagram shows the design of a HEP station.

The turbine is connected to a generator, which generates electricity.

Describe the energy transfers involved in generating electricity in the HEP station.

The HEP station is located near a large wind farm.

Give one advantage of generating electricity using the HEP station rather than the wind farm.

Give one disadvantage of generating electricity using the HEP station rather than the wind farm.

The HEP station has an electric pump that can pump water from the lower lake back to the upper lake.

The pump can be powered using electricity generated by the wind farm.

Explain how the HEP station and wind farm can be used together to maximise the effectiveness of generating electricity.

The photograph shows a toy called a marble run.

A student lifts a marble from the table to the top of the marble run at point A. They release the marble from point A and it rolls through pipes to reach the bottom of the marble run at point B.

The marble leaves the marble run at point B and rolls across the table.

As the marble rolls, energy is transferred due to the different forces acting on the marble.

Describe the energy transfers from before the student lifts the marble to when the marble reaches point B of the marble run.

The student wants to measure how much energy the marble loses as it moves from point A to point B.

The student needs to measure the speed of the marble as it leaves the marble run at point B.

Describe a method the student could use to measure this speed.

The difference in height between point A and point B is 0.21 m.

The mass of the marble is 5.5 g.

The marble leaves the marble run at point B with a speed of 0.76 m/s.

Calculate the energy lost by the marble as it rolls from point A to point B.

The circuit diagram shows a motor, power supply, switch and variable resistor connected in series.

The switch is open and the motor is not moving.

State how much energy is in the kinetic energy store of the motor.

The switch is closed.

The motor takes 0.42 seconds to reach its maximum speed of rotation.

The mean current in the motor is 3.9 A.

The voltage across the motor is 7.1 V.

Show that the work done on the motor during the 0.42 seconds is about 12 J.

Complete the Sankey diagram for the electric motor during the 0.42 seconds by giving the missing information.

store of surroundings

2 J

Use the Sankey diagram to calculate the efficiency of the process of bringing the motor to its maximum speed of rotation.

The driver of a racing car makes a pit stop during a race to change the tyres on the racing car.

The area where the tyres are changed is called the pit lane.

Before entering the pit lane, the speed of the car must decrease for safety reasons.

The mass of the racing car is 830 kg.

The maximum braking force is 41 000 N.

Show that the maximum deceleration of the racing car is approximately 50 m / s².

The racing car is travelling at an initial speed of 72 m / s.

Calculate the minimum distance needed to decrease the speed of the racing car from 72 m / s to 26 m / s.

The racing car slows down using its brakes.

The brakes work using friction.

The brakes become very hot when the racing car slows down.

Using ideas about energy, explain why the brakes become hot.

The tyres of the racing car also get very hot during a race.

A mechanic has to handle the hot tyres during the pit stop.

They wear protective gloves which have several layers of insulating materials.

Explain how the layers of insulating materials in the gloves reduce the risk of the mechanic burning their hands on the hot tyres.

This question is about different methods of generating electricity.

Natural gas can be burned to generate electricity.

Name the energy store that decreases when natural gas is burned.

Burning natural gas and the movement of water waves can both be used to generate electricity.

Discuss the advantages and disadvantages of these two methods of generating electricity.

A winch is used to pull a truck along a horizontal road.

The winch is connected to the truck by a thick rope.

The winch does 41 kJ of useful work on the truck when the truck is pulled a horizontal distance of 15 m.

State the formula linking work done, force and distance moved in the direction of the force.

Calculate the force that the rope exerts on the truck.

The winch includes a small engine. The engine burns petrol to power the motor in the winch.

The winch transfers energy mechanically to the truck.

The winch has an efficiency of 25% when pulling the truck.

Draw a Sankey diagram for this energy transfer.

The winch can also be used to pull the truck uphill at a constant speed.

The table gives some energy stores.

Add one tick () to each row to show what happens to the energy in each store as the truck is pulled uphill.

A teacher demonstrates the penetrating ability of alpha, beta and gamma radiation from some radioactive sources.

State a precaution the teacher should take to make sure they are working safely with the radioactive sources.

State the name of a detector the teacher could use to detect the radiation from each source.

Draw crosses () in the table to show which type of radiation cannot penetrate each material in the table.

An alpha particle of mass 6.610^–27kg travelling at a speed of 2.110⁷m/s hits a sheet of paper.

Calculate the kinetic energy (KE) of the alpha particle.

State the work done on the alpha particle when its speed is reduced to 0 m/s by the sheet of paper.

State which energy store of the paper increases when the alpha particle is stopped.

The photograph shows a vertical drop ride at an amusement park.

The car is pulled to the top of a vertical shaft and then released from rest.

The car then falls freely because of the force of gravity.

Calculate the speed of the car when it has fallen 18 m.

State the formula linking kinetic energy, mass and speed.

The mass of the car and its passengers is 2.1 tonnes.

Calculate the kinetic energy of the car when it has fallen 18 m.

[1 tonne = 1000 kg]

The actual speed of the car when it has fallen 18 m is lower than the value calculated in (a).

Describe the energy transfers occurring from immediately before the car was released to when the car has fallen 18 m.

Refer to stores and transfers in your answer.

The diagram shows part of the National Grid.

There is a step-up transformer at the power station end of a transmission line and a step-down transformer at a distant town.

Explain why step-up transformers and step-down transformers are used in this way.

State the formula linking the input voltage, the output voltage and the turns ratio for a transformer.

The primary coil on a step-up transformer has 3300 turns.

Calculate the number of turns required on the transformer’s secondary coil to step up the voltage from 15 kV to 340 kV.

Transformers in the National Grid have efficiencies less than 100%.

Suggest which energy store of the transformer increases as a result of the efficiency being less than 100%.

The iron core of a transformer is an electrical conductor.

When the transformer is in use, the primary coil causes a changing magnetic field in the iron core. This causes a small current to be induced in the core.

Explain how a current is induced in the core of the transformer.

Funcube-1 is a satellite that was launched into orbit around the Earth.

The rocket carrying Funcube-1 burns fuel to accelerate upwards.

As the rocket burns fuel, the energy in its chemical store reduces and the energy in its kinetic store and gravitational store changes.

State how the kinetic store of the rocket changes as the rocket burns fuel.

State how the gravitational store of the rocket changes as the rocket burns fuel.

The rocket engine stops burning fuel.

The rocket continues to go further away from the surface of the Earth.

The table gives some statements about the rocket’s energy stores.

Funcube-1 goes into a circular orbit above the surface of the Earth.

State the name of the force responsible for keeping Funcube-1 in orbit.

Funcube-1 has an orbital radius of 7100 km and an orbital period of 5800 s.

Calculate the orbital speed, in km / s, of Funcube-1.

orbital speed =_........ km / s

Funcube-1 spins and is heated by the Sun.

The diagram shows two coloured metal bars attached to a face of Funcube-1.

The surface of one metal bar is dull and black.

The surface of the other metal bar is shiny and white.

Temperature probes measure the temperature of each metal bar.

Use ideas about thermal energy transfer to explain how the temperature of each metal bar changes as Funcube-1 spins.

A racing car uses an engine and an electric motor to power its wheels.

The electric motor can only operate at maximum power for part of each lap of the race.

The electric motor has a maximum power output of 1.210⁵W.

The electric motor transfers 4.010⁶J of energy when it operates at maximum power.

Calculate the amount of time the electric motor can operate at maximum power.

The diagram shows a simplified view of a direct current (d.c.) electric motor.

State what is meant by the term direct current.

Explain the purpose of the brushes and the commutator in the d.c. motor.

The electric motor in the racing car can also be used as a generator to charge a battery pack. It is known as a motor generator unit (MGU).

The rotating wheels of the car cause the magnets in the MGU to spin near a coil of wire.

This induces a current in the coil when the coil is connected to the battery pack.

Name the energy store of the battery pack that increases when the battery pack is being charged.

Explain why the kinetic energy store of the car must decrease when the MGU charges the battery pack.

A student uses this apparatus to investigate the stretching of a rubber band.

This is the student’s method.

● attach the 12 cm long rubber band to a clamp stand

● hang a 1 N weight from the other end of the rubber band

● determine the extension of the rubber band

The student repeats this method, increasing the weight by 1 N each time until the weight is 10 N.

Describe how the student could determine the extension of the rubber band.

The graph shows the student’s results.

Explain how the graph shows that the rubber band does not obey Hooke’s Law.

The area under the curve on the graph is equal to the increase in the rubber band’s elastic energy store.

Estimate the increase in the rubber band’s elastic energy store when the rubber band has been extended by 20 cm.

The photograph shows the Three Gorges Dam in China, one of the largest hydroelectric power stations on Earth.

State two advantages of generating electricity using hydroelectric power stations.

Water is held in a reservoir on one side of the dam.

The water flows through turbines to a river on the other side of the dam.

The water level of the river is lower than the water level of the reservoir.

State which energy store of the water decreases as the water flows from the reservoir to the river.

How is energy transferred from the dam to homes and factories in China?

The Three Gorges Dam has a larger maximum output power than any other hydroelectric power station on Earth.

State what is meant by the term power.

The mean energy transferred by the dam each day is 9.710¹⁴ J.

Calculate the mean output power of the dam.

The maximum output power is 22 500 MW.

Which of these is the same as 22 500 MW?

Suggest why the Three Gorges Dam does not always operate at its maximum output power.

The boxes give some situations and some energy stores.

Draw one straight line from each situation to the energy store that decreases for that situation.

The first one has been done for you.

Energy is transferred when a filament lamp is connected to a battery.

Which method of energy transfer takes place between the battery and the lamp?

Which method of energy transfer takes place between the lamp and the surroundings?

State Hooke’s Law.

The graph shows how the extension of a rubber band varies with the force applied.

Explain how the graph shows that the rubber band does not obey Hooke’s Law.

Diagram 1 shows a model aeroplane powered by a rubber band.

A person rotates the propeller of the model aeroplane, which twists the rubber band.

He then releases the propeller and it spins.

Energy transfer occurs during this process.

The box lists words associated with energy.

Use words from the box to complete the passage.

The person does_........ work to twist the rubber band.

As the person twists the rubber band it extends, increasing the_........

energy store of the rubber band. When the rubber band is released it does mechanical work,

increasing the_........ energy store of the propeller.

Diagram 2 shows the aeroplane flying horizontally to the right.

Diagram 2

The aeroplane flies at a constant speed.

Diagram 2 shows two forces acting on the aeroplane.

Draw labelled arrows on diagram 2 to show two more forces acting on the aeroplane.

Energy is transferred from the Sun to the Earth.

Nuclear fusion happens in the Sun.

Which energy store of the Sun decreases during nuclear fusion?

How is energy transferred through space from the Sun to the Earth?

Solar panels use energy from the Sun to heat water.

The total area of the solar panels is 15 m².

Each 1.0 m² of the solar panels receives 1000 J of energy per second from the Sun.

Show that the total energy transferred to the solar panels in 2 hours is about 100 MJ.

A mass of 1100 kg of cold water is in the solar panels at an initial temperature of 20C.

Calculate the final temperature of this water after it has been heated by the Sun for 2 hours.

[specific heat capacity of water = 4200 J/kg C]

final temperature _........ C

Give a reason why the actual final temperature of the water will be lower than the calculated value.

Conventional power stations burn fuel in a furnace.

The fuel can be a solid, a liquid or a gas.

Describe the motion of particles in a solid, a liquid and a gas.

When the fuel is burned, energy is transferred from the fuel to the water.

The water boils and turns into steam.

Describe how energy stored in the fuel is transferred to the water.

Refer to energy stores and transfers in your answer.

The temperature-time graph shows how the temperature of the water changes as it is heated in the furnace at a constant rate.

Explain how the graph shows that the water changes state as it is heated.

This question is about energy resources.

The table lists some methods of generating electricity using energy resources.

Place ticks () in the table to show if each method uses a renewable energy resource. One has been done for you.

Solar cells can be used to generate electricity.

How is energy transferred from the Sun to a solar cell?

State one disadvantage of using solar cells to generate electricity.

The graph shows how the velocity of a parachute jumper changes with time.

At point A, the parachute jumper is falling at terminal velocity and has not yet opened her parachute.

Which statement is correct about the parachute jumper at point A?

Which is the best estimate of the distance fallen by the parachute jumper from the start until point A?

The parachute jumper opens her parachute at point B.

Her velocity decreases until she reaches terminal velocity again at point C.

Explain this change in velocity.

After point C, the parachute jumper continues to fall at a constant velocity.

As she falls, energy is transferred from a gravitational store.

Which store is the energy transferred into?

The diagram shows a fossil fuel power station.

Five stages of electricity generation and transmission are shown.

furnace and boiler condenser turbines generator transformer

The power station burns a fossil fuel in the furnace.

Give an example of a fossil fuel.

Which stage of the power station transfers energy from a chemical store to a thermal store?

Which stage of the power station transfers energy electrically from a kinetic energy store?

Electricity can also be generated by solar farms.

Energy is transferred from the Sun to the solar farm by radiation.

The solar farm uses photovoltaic cells to transfer this energy electrically.

Discuss the advantages and disadvantages of generating electricity using solar farms.