Efficiency

Which of these describes the motion of particles in a liquid?

A student is asked to find the density of a metal key.

Figure 8 shows a metal key and some apparatus.

Using the apparatus shown in Figure 8, describe how the student can find the density of the metal key.

A student heats an aluminium block, as shown in Figure 9.

The aluminium block has a mass of 0.96 kg.

The specific heat capacity of aluminium is 920 J / kg °C.

The temperature of the block increases from 18 °C to 35 °C.

Calculate the change in thermal energy of the aluminium block.

Use the equation

change in thermal energy = mass × specific heat capacity × change in temperature

change in thermal energy =_........

Suggest one way the student could reduce the energy loss from the aluminium block during the experiment.

The thermometer does not show the maximum temperature reached by the aluminium block until some time after the heater is switched off.

Give one reason for this.

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 14 shows a saucepan of milk being heated on an electric cooker.

Figure 14

Figure 15 is a table of data about the milk being heated.

Using data from the table in Figure 15, calculate the increase in temperature of the milk.

increase in temperature =_........

Using data from the table in Figure 15, calculate the specific heat capacity of the milk.

Use the equation

specific heat capacity =_........ J/kg °C

The cooker supplies 130 000 J of energy in a time of 87 s.

Calculate the power supplied by the cooker.

Use the equation

Give your answer to 2 significant figures.

power =_........

The cooker supplies 130 000 J of energy but only 96 000 J of this energy is used to heat the milk.

Calculate the efficiency of heating the milk using this cooker.

Use the equation

The wiring for the cooker has safety features.

Which of these wires would help to protect a person from getting an electric shock if a fault developed in the cooker?

Explain how a fuse can prevent overheating of the wiring for the cooker.

Figure 17 shows an athlete training with a push sled.

The athlete pushes the sled with a force of 645 N.

Calculate the distance the sled moves when the force of 645 N does 7440 J of work on the sled.

Give your answer to an appropriate number of significant figures.

distance moved =_........

Figure 18 shows an electric motor lifting a set of masses.

Describe an experiment, using the apparatus in Figure 18, to determine the gravitational potential energy gained by the masses as they are lifted.

Your description should include any measuring devices to be used.

You may add to the diagram in Figure 18 if it helps your answer.

In one experiment, the change in gravitational potential energy of the masses was 5.8 J.

The total mass lifted was 320 g.

Calculate the vertical height the masses travelled through.

Use g = 10 N/kg.

height =_........

The efficiency of the motor was 59%.

State one reason why the motor was not 100% efficient.

Which of these changes of state describes sublimation?

Figure 21 shows a sealed aerosol can.

The sealed can is taken from a cold room into a warm room.

If the volume of the can remains the same, which of these does not change?

Figure 22 shows a storage heater.

The storage heater contains bricks.

The bricks are heated electrically.

The electrical heater supplies 210 kJ of energy to each brick in the storage heater.

One brick has a mass of 5.8 kg.

The specific heat capacity for the brick is 860 J/kg K.

Use this data to calculate the increase in temperature of the brick.

temperature increase =_........

The actual temperature increase will be smaller than you calculated in (i).

Explain why the actual temperature increase will be smaller than the value in (i).

* (d) Describe an investigation to determine the value for the specific heat capacity of water.

Your answer should include details of

• the apparatus needed

• the experimental procedure

• how the value may be calculated from the measurements taken.

You may draw a diagram to help your answer.

Figure 20 shows a Mars rover, a vehicle used for exploring the surface of the planet Mars.

(Source: © BEST-BACKGROUNDS/Shutterstock)

Figure 20

The power supply in a Mars rover is called an RTG.

The RTG contains a radioactive isotope that releases thermal energy as it decays.

The RTG uses the thermal energy released in the decay to provide electrical power for the rover.

An RTG has an efficiency rating of only 7%.

Calculate the useful energy transferred by the RTG when 1300 J of thermal energy is released in the decay.

Use the equation useful energy transferred by the device efficiency = × 100% total energy supplied to the device

Suggest, with a reason, one property the isotope must have to be suitable for use in the RTG.

Figure 21 shows the fission of a uranium nucleus.

Nuclear fission
free neutron

(Source: adapted from © 1501926062/Shutterstock)

Figure 21

The total mass of all the particles after the reaction is less than the total mass of the particles before the reaction.

The energy released in the reaction comes from the change in mass.

This is shown in the equation

energy released = (change in mass) × (speed of light)²

The energy released in one fission reaction = 1.49 × 10^–10J.

The speed of light = 3.00 × 10⁸m / s.

Calculate the change in mass.

*(c) The energy released in a single uranium fission is very small.

In a nuclear power station, the fission of uranium in the reactor releases large amounts of energy.

The energy released is enough to generate electricity for thousands of homes.

The demand for electricity varies.

Explain

• how large amounts of energy can be released in the reactor

• how the rate of energy release is controlled as the demand for electricity varies.

Equations

Which of these means changing state from solid directly to gas?

An object has a mass of 7.22×10^–2kg and a volume of 2.69×10^–5m³.

Calculate the density, ρ, of the object.

Use the equation

State the unit.

Aluminium has a melting point of 660C.

The absolute zero of temperature is –273C.

Calculate the melting point of aluminium in kelvin.

melting point of aluminium =_........

Describe the motion of particles in liquid aluminium (above 660C).

*(d) The table shows some properties of two materials used as thermal insulation.

The higher the R‑value, the better the thermal insulating properties of the material.

Assess which of these materials may be the more suitable to use as thermal insulation in a building.

Your answer should compare the properties of fibreglass and polystyrene given in the table.

Figure 21 shows a pulley system that enables a person to lift a heavy barrel.

The person pulls down on the rope to make the barrel rise through 1.2 m.

The work done against gravity on the barrel is 1800 J.

Calculate the weight of the barrel.

Use the equation

work done = forcedistance moved in the direction of the force

weight of the barrel =_........

The efficiency of the system is 64%.

Calculate the total work done by the person.

Use the equation

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

Some energy is wasted due to friction.

Suggest another reason why some energy is wasted in using this pulley system.

*(b) A student has the equipment shown in Figure 22.

Devise an experiment to investigate how the efficiency of the pulley system varies with the weight of metal being lifted.

Your answer should include how you will use your measurements.

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

Which statement describes conservation of energy in a closed system?

A student uses the apparatus in Figure 3 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 4 shows how the thermal conductivity of expanded polystyrene changes with the density of expanded polystyrene.

density of expanded polystyrene in kg/m³

Figure 4

Using the graph in Figure 4, describe how the thermal conductivity of expanded polystyrene changes with the density of expanded polystyrene.

This question is about waves in the electromagnetic (e.m.) spectrum.

The potential danger associated with the waves of the e.m. spectrum increases as

A microwave oven uses waves of frequency 2.45 GHz.

Calculate the wavelength of the microwaves.

The microwave oven is 55% efficient and transfers 42 000 J of energy to some food when it is heated.

Calculate the total amount of energy that must be supplied to the oven.

*(c) X-rays and radio waves are part of the electromagnetic spectrum and have different uses.

These radiations are produced in different ways.

X-rays are emitted when electrons within an atom go through energy changes.

Radiowaves are produced by electrons in circuits.

Compare X-rays with radio waves.

Your answer should refer to

• the uses of both types of radiation

• the different ways that electrons are involved in producing X-rays and radio waves.

An electric water pump is powered by the 230 V mains supply.

Figure 12 shows the inside of the plug on the cable to the pump.

One wire in the plug is the earth wire.

The other two wires are

Describe the purpose of the component labelled X.

The 230 V mains supply transfers 9000 J of energy to the pump motor in 1 minute.

Calculate the current in the pump motor.

Use the equation

The system transfers 8400 J of useful kinetic energy to the water passing through the pump in 1 minute.

Figure 13 shows a diagram of the energy transfers.

Explain why the useful energy transferred to the water is different from the total energy supplied to the pump.

Calculate the efficiency of the pump.

Use the equation

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:

Figure 13 shows wind turbines, used to generate electricity for the National Grid.

The wind turns the turbine blades.

The wind is a renewable source of energy.

State two other renewable sources of energy.

For one turbine

• the energy input per second from the wind is 6.2 kJ

• the energy output per second to the National Grid is 2.2 kJ.

Calculate the efficiency of this turbine.

Suggest a reason why it is impossible for the turbine to use all the kinetic energy of the wind.

*(b) Nuclear fission and nuclear fusion are two non-renewable sources of energy.

Compare nuclear fission and nuclear fusion as possible sources of energy for generating electricity using a nuclear reactor.

Your comparison should refer to

• the differences between nuclear fission and nuclear fusion

• the relative advantages and difficulties involved in using these sources.

Describe, in terms of particles, two differences between a solid and a liquid of the same substance.

Figure 20 shows the dimensions of a solid block of concrete.

Density of concrete, ρ, = 2100 kg / m³.

Calculate the mass of the concrete block.

Use the equation:

m = ρ × V

mass of concrete block =_........

Figure 21 shows a shed made mostly of concrete blocks.

State two practical ways to reduce heat loss from this shed.

*(d) A student has two metal strips and a ruler, as shown in Figure 22.

A teacher tells the student that

• one metal strip is made of aluminium

• the other metal strip is made of stainless steel.

The student looks up data in a reference book, finding some density values:

density of aluminium = 2710 kg / m³

density of stainless steel = 7850 kg / m³

The student has access to more of the same metal strips, if needed, and may ask for any extra measuring devices.

Plan how the student could confirm the teacher’s statements, by determining the density of each of the strips as accurately as possible.

Describe, in terms of particles, two differences between a solid and a liquid of the same substance.

Figure 6 shows the dimensions of a solid block of concrete.

Density of concrete, ρ, = 2100 kg / m³.

Calculate the mass of the concrete block.

Use the equation

m = ρ × V

Figure 7 shows a shed made mostly of concrete blocks.

State two practical ways to reduce heat loss from this shed.

On a very cold day, the temperature of the air is −4 °C.

Calculate the value of this temperature on the kelvin scale.

Two cyclists ride on a hilly road and go through points P, Q, R and S.

The diagram in Figure 16 shows how the vertical height of the road changes during the journey from P to S.

The greatest overall change in gravitational potential energy for each cyclist is between which two points on the journey?

The total weight of one cyclist and bicycle is 700 N.

Calculate the total amount of work done against gravity when the cyclist travels from point P to point Q in the journey.

The gravitational potential energy of the other cyclist changes by 11 250 J when travelling from point Q to point R.

Calculate the mass of this cyclist.

Gravitational field strength = 10 N / kg

Use the equation

∆ GPE = m × g × ∆ h

Explain why the total amount of work done by a cyclist between points Q and R is different from the change in gravitational potential energy of the cyclist between points Q and R.

The cyclists lubricated the chains and the wheel bearings of their bicycles before setting off.

Lubricating the chains and wheel bearings helps to

The kinetic energy of another cyclist is 2800 J.

The mass of the cyclist is 85 kg.

Calculate the velocity of this cyclist.

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.

A kettle is used to heat water.

Figure 11 shows a graph of temperature against time for the water in the kettle.

Calculate the rate of increase in temperature at a time of 150 s, by drawing a tangent to the curve in Figure 11 at a time of 150 s.

The kettle has an efficiency of 91% in supplying energy to the water. The thermal energy of the water increases by 3.3 × 10⁵J in 200 s.

Calculate the total amount of energy supplied to the kettle in the 200 s.

Use the equation

total amount of energy supplied =_........

*(c) The global demand for electricity is increasing.

There is a debate about whether nuclear power generation should or should not contribute to meeting this increasing demand.

Discuss the arguments for and against using nuclear power to meet the increasing global demand for electricity.

Figure 6 shows two gears.

Gear R and gear S can rotate.

Gear R has 20 teeth.

Gear S has 60 teeth.

Gear S rotates through 2 complete revolutions.

Calculate how many complete revolutions gear R rotates by.

gear R has rotated through_........ revolutions

Figure 7 shows two gears, S and T.

Gear S can rotate on a fixed axle.

Gear T can move up and down.

Gear S has 60 teeth.

The distance between each of the teeth on gear S and on gear T is 2 mm.

Gear S moves through one complete revolution in the direction shown.

Which of these describes the motion of gear T?

Figure 8 shows a force of 70 N turning a lever about point P.

Calculate the moment of the 70 N force about point P.

State the unit.

Use the equation

moment = force × distance normal to the direction of the force

Figure 9 shows a worker using a wheelbarrow to move some sand.

The load is equal to the total weight of the sand and the wheelbarrow.

The effort is the force that the worker applies to the wheelbarrow handles.

The worker applies just enough effort to lift the load.

Explain why the effort is smaller than the load.

Some sand falls down and sticks between the wheel and the axle.

State why it might be harder to push the wheelbarrow along when there is some sand between the wheel and the axle.

Figure 19 shows a small piece of copper about 3 cm high.

A student wants to determine the density of copper.

The student uses a balance to measure the mass of the piece of copper.

Explain how the student could measure the volume of the piece of copper.

The mass of the piece of copper is 0.058 kg.

The volume of the piece of copper is 6.510^–6m³.

Calculate the density of copper.

A student wants to determine the specific heat capacity of copper.

Figure 20 shows a piece of copper, with a thread tied around it, in a glass beaker of boiling water.

The student leaves the piece of copper in the boiling water so that the copper reaches a temperature of 100C.

The student uses the thread to take the piece of copper out of the boiling water.

The student puts the hot piece of copper into a different beaker of cold water at 20C.

The apparatus is shown in Figure 21.

The student assumes that the thermal energy gained by the water equals the thermal energy lost by the piece of copper.

The water and copper both reach a temperature of 22C.

The cold water gains 1050 J of energy.

The mass of the piece of copper is 0.058 kg.

Calculate a value for the specific heat capacity of copper, using these results.

Use the equation

change in thermal energy = massspecific heat capacitychange in temperature

The value for the specific heat capacity of copper obtained from the student’s results is lower than the correct value.

State two ways that the experiment could be improved to give a value that is closer to the correct value.

A long piece of wire is made into a coil as shown in Figure 22.

The coil is connected to a low voltage power supply.

Describe how this coil could be used instead of the Bunsen burner in Figure 20.

Figure 4 shows a small piece of copper about 3 cm high.

A student wants to determine the density of copper.

The student uses a balance to measure the mass of the piece of copper.

Explain how the student could measure the volume of the piece of copper.

The mass of the piece of copper is 0.058 kg.

The volume of the piece of copper is 6.5×10^–6m³.

Calculate the density of copper.

A student wants to determine the specific heat capacity of copper.

Figure 5 shows a piece of copper, with a thread tied around it, in a glass beaker of boiling water.

The student leaves the piece of copper in the boiling water so that the copper reaches a temperature of 100C.

The student uses the thread to take the piece of copper out of the boiling water.

The student puts the hot piece of copper into a different beaker of cold water at 20C.

The apparatus is shown in Figure 6.

The student assumes that the thermal energy gained by the water equals the thermal energy lost by the piece of copper.

The water and copper both reach a temperature of 22C.

The cold water gains 1050 J of energy.

The mass of the piece of copper is 0.058 kg.

Calculate a value for the specific heat capacity of copper, using these results.

Use the equation

change in thermal energy = massspecific heat capacity×change in temperature

The value for the specific heat capacity of copper obtained from the student’s results is lower than the correct value.

State two ways that the experiment could be improved to give a value that is closer to the correct value.

Figure 19 shows four forces, P, Q, R and S, acting on a rod.

The rod can rotate around an axle.

Which force will make the rod rotate about the axle?

Figure 20 shows a person trying to lift a large rock using a metal bar.

The rock weighs 1800 N.

The person can only produce a downwards force of 600 N.

The person cannot lift the rock.

Explain, using calculations, why the person cannot lift the rock.

Explain one change to the arrangement that will make it possible for this person to lift the rock.

Figure 21 shows a bicycle.

The rider uses the pedals to make the large gear wheel turn.

The large gear wheel moves the chain. The chain turns the small gear wheel.

The large gear wheel has 48 teeth.

The small gear wheel has 12 teeth.

The large gear wheel turns 2 times each second.

Calculate the number of times that the small gear wheel turns each second.

_........ turns each second

Explain how the oil improves the efficiency of the bicycle.

Figure 6 shows four forces, P, Q, R and S, acting on a rod.

The rod can rotate around an axle.

Which force will make the rod rotate about the axle?

Figure 7 shows a person trying to lift a large rock using a metal bar.

The rock weighs 1800 N.

The person can only produce a downwards force of 600 N.

The person cannot lift the rock.

Explain, using calculations, why the person cannot lift the rock.

Explain one change to the arrangement that will make it possible for this person to lift the rock.

Figure 8 shows a bicycle.

The rider uses the pedals to make the large gear wheel turn.

The large gear wheel moves the chain. The chain turns the small gear wheel.

The large gear wheel has 48 teeth.

The small gear wheel has 12 teeth.

The large gear wheel turns 2 times each second.

Calculate the number of times that the small gear wheel turns each second.

_........ turns each second

Explain how the oil improves the efficiency of the bicycle.

State two non‑renewable energy sources.

Figure 9 shows the renewable energy sources used in the UK in 2015.

Figure 9 is to scale.

State the energy source that gave the greatest amount of renewable energy for the UK in 2015.

Justify your choice of energy source in part (i).

State which of these energy sources gave about 20% of the energy from renewable sources for the UK in 2015.

Figure 10 shows all the energy sources used in Canada in 2014 and a

effect on the environment_........

effect on the environment_........

Figure 11 shows a wind turbine.

Explain how unwanted energy transfers could be reduced in the gear box.

Figure 14 shows the vertical forces on an aeroplane.

Use information from the diagram to determine the size and direction of the resultant vertical force on the aeroplane.

The aeroplane is descending.

Figure 15 shows a diagram of the resultant vertical and horizontal forces on the aeroplane as it is descending.

Complete the diagram to show the resultant of these two forces.

The mass of the aeroplane is 750 kg.

Calculate the change in gravitational potential energy of the aeroplane as it descends from 1300 m to the ground.

Gravitational field strength (g) = 10 N/kg

The aeroplane is powered by an engine that burns fuel.

The fuel supplies a total of 6500 kJ of energy every minute.

The efficiency of the engine is 0.70 (70%).

Calculate the power output of the engine.

Give your answer in kW.

Explain why the efficiency of the engine is less than 1 (100%).