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 3 shows a metal key and some apparatus.

Using the apparatus shown in Figure 3, describe how the student can find the density of the metal key.

A student heats an aluminium block, as shown in Figure 4.

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 9 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

h =_........ m

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

velocity =_........ m/s

Figure 10 is a diagram that represents energy changes from P to Q.

State what is represented by X.

Calculate the value of X.

value of X =_........ J

Calculate the efficiency of the system represented in Figure 10.

efficiency =_........

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 1 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

h =_........ m

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

velocity =_........ m/s

Figure 2 is a diagram that represents energy changes from P to Q.

State what is represented by X.

Calculate the value of X.

value of X =_........ J

Calculate the efficiency of the system represented in Figure 2.

efficiency =_........

Figure 8 shows a saucepan of milk being heated on an electric cooker.

Figure 8

Figure 9 is a table of data about the milk being heated.

Using data from the table in Figure 9, calculate the increase in temperature of the milk.

increase in temperature =_........ °C

Using data from the table in Figure 9, 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 =_........ W

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

efficiency =_........

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 8 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 =_........ m

Figure 9 shows an electric motor lifting a set of masses.

Describe an experiment, using the apparatus in Figure 9, 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 9 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 =_........ m

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 12 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 13 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 =_........ °C

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.

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.

density =_........ 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 =_........ K

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.

Equations

Figure 11 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 =_........ N

The efficiency of the system is 64%.

Calculate the total work done by the person.

Use the equation

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

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 12.

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 9 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 10 shows how the thermal conductivity of expanded polystyrene changes with the density of expanded polystyrene.

density of expanded polystyrene in kg/m³

Figure 10

Using the graph in Figure 10, describe how the thermal conductivity of expanded polystyrene changes with the density of expanded polystyrene.

Figure 11 is an energy diagram for an electric kettle, used to heat water.

one second = 2400 J

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

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

Calculate the efficiency of the kettle.

Use the equation

efficiency =_........

Which statement describes conservation of energy in a closed system?

A student uses the apparatus in Figure 1 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 2 shows how the thermal conductivity of expanded polystyrene changes with the density of expanded polystyrene.

density of expanded polystyrene in kg/m³

Figure 2

Using the graph in Figure 2, 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.

wavelength =_........ m

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.

energy supplied to oven =_........ J

*(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 5 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

current =_........ A

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

Figure 6 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

efficiency =_........

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

gain in gravitational potential energy =_........ J

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

kinetic energy =_........ J

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.

energy wasted =_........ J

Calculate the efficiency of the electric motor.

Use the equation:

efficiency of electric motor =_........

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

Figure 13 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 =_........ kg

Figure 14 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 15.

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 3 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 =_........ kg

Figure 4 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.

temperature =_........ K

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

The diagram in Figure 7 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.

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

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

mass =_........ kg

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

velocity =_........ m / s

A student lifts a toy car from a bench and places the toy car at the top of a slope as shown in Figure 9.

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 9 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.

density of copper =_........ kg/m³

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

Figure 10 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 11.

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

specific heat capacity of copper from these results =_........ J/kgC

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 12.

The coil is connected to a low voltage power supply.

Describe how this coil could be used instead of the Bunsen burner in Figure 10.

Figure 1 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.

density of copper =_........ kg/m³

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

Figure 2 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 3.

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

specific heat capacity of copper from these results =_........ J/kgC

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.

State two non‑renewable energy sources.

Figure 5 shows the renewable energy sources used in the UK in 2015.

Figure 5 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 6 shows all the energy sources used in Canada in 2014 and a

change 1_........

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

change 2_........

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

Figure 7 shows a wind turbine.

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

Which of these is a non-renewable source of energy?

Explain why renewable sources provide an increasing fraction of the electricity supply for many countries.

Electricity can be generated using a water turbine.

Water gains kinetic energy by falling from the top of a dam.

Calculate the minimum height that 7.0 kg of water must fall to gain 1300 J of kinetic energy.

minimum height =_........ m

As water enters the turbine at the bottom of the dam, the kinetic energy of 8.0 kg of moving water is 1100 J.

Calculate the speed of the moving water as it enters the turbine.

speed =_........ m/s

Moving air can be used to generate electricity using a wind turbine.

Figure 6 is a graph of kinetic energy against wind speed for a mass of moving air.

Just before the air reaches a wind turbine it has a wind speed of 15 m/s.

When the air has gone through the turbine it has a wind speed of 13 m/s.

As the air moves through the turbine some of its kinetic energy is transferred to the turbine.

Use the graph to determine the percentage of the kinetic energy transferred to the turbine from the air.

percentage of kinetic energy transferred from the air =_........ %

Which of these forces keeps the Moon moving around the Earth?

Which of these is a scalar quantity?

Figure 4 shows a box at rest on a floor.

The force that the floor exerts on the box is shown by the vector in Figure 4.

Figure 4

Add another vector to the diagram in Figure 4 to show the weight of the box.

Figure 5 shows part of a cart.

When the wheels turn the axles become warm.

Explain why the axles become warm when the wheels turn.

Give one way of reducing the heating of the axles when the wheels turn.

Complete the equation that relates efficiency, useful energy transferred by a device and total energy supplied to the device.

In one second an engine has a total energy input of 7500 J.

In one second 3200 J is transferred to the surroundings as wasted energy.

Calculate the useful energy transferred by the engine.

useful energy transferred =_........ J

Calculate the efficiency of this engine.

efficiency of the engine =_........

Figure 5 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.

size =_........ kN, direction is_........

The aeroplane is descending.

Figure 6 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

energy =_........ J

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.

power =_........ kW

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