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Energy stores and transfers: GCSE Combined Science Physics practice questions

Foundation and Higher · Grade 5

A second set of questions on energy stores and transfers. They are different from the ones on the topic page. Try each, then open the answer and compare your working.

More questions

Question 1 Hard

Aisha tests a motor. The useful energy is 250 J and the total input is 1000 J. Calculate the efficiency as a percentage.

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Answer: 25%

  1. efficiency = useful ÷ total × 100
  2. 250 ÷ 1000 × 100 = 25%

Question 2 Hard

A heater transfers 50 J usefully from 200 J input. Work out the efficiency.

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Answer: 25%

  1. efficiency = useful ÷ total × 100
  2. 50 ÷ 200 × 100 = 25%

Question 3 Hard

Jonah drops a 2 kg ball through 8 m. Assume no air resistance and g = 10 N/kg. (a) Calculate the gravitational potential energy lost. [2 marks] (b) Calculate the speed at the bottom. Give your answer to 2 significant figures. [3 marks]

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Answer: (a) 160 J (b) 13 m/s

  1. gpe = 2 × 10 × 8 = 160 J
  2. ke = gpe, so 0.5 × 2 × v² = 160
  3. v² = 2 × 160 ÷ 2 = 160
  4. v = √160 = 13 m/s

Question 4 Hard

Priya's winch transfers 500 J in 40 s. Calculate the power.

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Answer: 12.5 W

  1. power = energy ÷ time
  2. 500 ÷ 40 = 12.5 W

Question 5 Hard

Use of wind power has risen over twenty years. Give one reason for this trend.

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Answer: to reduce carbon dioxide emissions

  1. Wind turbines do not burn fuel.
  2. They help to reduce carbon dioxide emissions.

Quick checks

Short questions with options. Choose one before you open the answer.

Check 1

What is the unit of energy?

  1. The joule, J
  2. The watt, W
  3. The newton, N
Show answer

The joule, J Energy is measured in joules, J.

Check 2

What is the unit of power?

  1. The joule, J
  2. The watt, W
  3. The kilogram, kg
Show answer

The watt, W Power is measured in watts. One watt is one joule per second.

Check 3

Which store holds the energy of a book on a high shelf?

  1. The kinetic store
  2. The elastic potential store
  3. The gravitational potential store
Show answer

The gravitational potential store It could fall, so its energy is in the gravitational potential store.

Check 4

Which store holds the energy of a moving bike?

  1. The kinetic store
  2. The thermal store
  3. The chemical store
Show answer

The kinetic store Moving things have energy in their kinetic store.

Check 5

Which store holds the energy in a squashed spring?

  1. The gravitational potential store
  2. The elastic potential store
  3. The nuclear store
Show answer

The elastic potential store A squashed spring is deformed, so the energy is in its elastic potential store.

Check 6

Which store holds the energy in a battery or a bar of chocolate?

  1. The thermal store
  2. The kinetic store
  3. The chemical store
Show answer

The chemical store Fuels, food and batteries keep energy in a chemical store.

Check 7

Write the equation for gravitational potential energy.

  1. gpe = 0.5 × mass × height²
  2. gpe = mass × g × height
  3. gpe = mass × height ÷ g
Show answer

gpe = mass × g × height Gravitational potential energy = mass × gravitational field strength × height.

Check 8

Write the equation for kinetic energy.

  1. ke = mass × speed
  2. ke = mass × g × speed
  3. ke = 0.5 × mass × speed²
Show answer

ke = 0.5 × mass × speed² Kinetic energy = 0.5 × mass × speed squared.

Check 9

What does g stand for, and what value do we take?

  1. Gravitational field strength, 10 N/kg
  2. Gravity speed, 10 m/s
  3. Gram, 1000 g in a kg
Show answer

Gravitational field strength, 10 N/kg Take g = 10 N/kg on Earth in these calculations.

Check 10

How do you calculate power from energy and time?

  1. Power = energy × time
  2. Power = energy transferred ÷ time
  3. Power = time ÷ energy
Show answer

Power = energy transferred ÷ time Power is the energy transferred each second: P = E ÷ t.

Check 11

How many joules does a 60 W bulb transfer every second?

  1. 6 J
  2. 3600 J
  3. 60 J
Show answer

60 J 1 W = 1 J/s, so 60 W transfers 60 J each second.

Check 12

How do you calculate efficiency as a percentage?

  1. Useful output ÷ total input × 100
  2. Total input ÷ useful output × 100
  3. Wasted energy ÷ total input × 100
Show answer

Useful output ÷ total input × 100 Efficiency = useful energy out ÷ total energy in, times 100.

Check 13

What does dissipated mean for energy?

  1. Destroyed completely
  2. Spread out into the surroundings, usually as heat
  3. Stored in a spring
Show answer

Spread out into the surroundings, usually as heat Dissipated energy ends up in the thermal store of the surroundings, where it is not useful.

Check 14

What happens to the energy wasted by friction?

  1. It is destroyed
  2. It goes into the nuclear store
  3. It is transferred to the thermal store of the surroundings
Show answer

It is transferred to the thermal store of the surroundings Friction makes things warm, so the energy goes to the thermal store.

Check 15

What does conservation of energy mean?

  1. Energy cannot be created or destroyed, only transferred, stored or dissipated
  2. Energy is saved by switching things off
  3. Energy is used up when it does work
Show answer

Energy cannot be created or destroyed, only transferred, stored or dissipated The total energy before always equals the total energy after.

Check 16

What is a closed system?

  1. A system with the door shut
  2. A system where no energy enters or leaves
  3. A system with no moving parts
Show answer

A system where no energy enters or leaves In a closed system the total energy stays the same.

Check 17

A box is lifted twice as high with the same mass. What happens to its gpe?

  1. It stays the same
  2. It goes up four times
  3. It doubles
Show answer

It doubles gpe is proportional to height, so twice the height gives twice the energy.

Check 18

A trolley doubles its speed. What happens to its kinetic energy?

  1. It goes up four times
  2. It doubles
  3. It stays the same
Show answer

It goes up four times Double the speed gives 2² = 4 times the kinetic energy.

Check 19

A student says: "The brakes destroy the energy of the bike." What is wrong?

  1. Energy is transferred to the thermal store, not destroyed
  2. The brakes add energy to the bike
  3. The bike has no energy to destroy
Show answer

Energy is transferred to the thermal store, not destroyed Friction in the brakes transfers kinetic energy to the thermal store of the brakes and the air.

Check 20

A student works out an efficiency of 250%. What is wrong?

  1. Nothing, it is a very good machine
  2. Efficiency cannot be above 100%, so the sum was upside down
  3. The answer should be in joules
Show answer

Efficiency cannot be above 100%, so the sum was upside down More than 100% would mean energy was created. Divide useful by total, not total by useful.

Check 21

A student calculates gpe for a 500 g mass by using 500 in the equation. What is wrong?

  1. The mass must be in newtons
  2. Nothing is wrong, grams are fine
  3. The mass must be in kg, so use 0.5
Show answer

The mass must be in kg, so use 0.5 Divide grams by 1000 to get kilograms before using the equation.

Check 22

Why is the kinetic energy at the bottom of a slope often less than the gpe lost at the top?

  1. Friction and air resistance dissipate some energy
  2. Gravity gets weaker on the way down
  3. Some energy is destroyed
Show answer

Friction and air resistance dissipate some energy The missing energy is in the thermal store of the surroundings.

Check 23

A kettle is rated at 2000 W. How much energy does it transfer in 10 s?

  1. 200 J
  2. 20 000 J
  3. 2010 J
Show answer

20 000 J E = P × t = 2000 × 10 = 20 000 J.

Check 24

A machine takes in 50 J and gives out 20 J of useful energy. How much is wasted?

  1. 70 J
  2. 20 J
  3. 30 J
Show answer

30 J Wasted energy = 50 − 20 = 30 J.

Check 25

What is a system in physics?

  1. Only a machine with a motor
  2. An object or a group of objects
  3. A source of energy
Show answer

An object or a group of objects An object or a group of objects.

Check 26

A ball is thrown upwards. Which energy store fills as it rises?

  1. The elastic potential store
  2. The nuclear store
  3. The gravitational potential store
Show answer

The gravitational potential store Its gravitational potential store.

Check 27

A car brakes to a stop. Which store gains the energy?

  1. The thermal store of the brakes
  2. The chemical store of the fuel
  3. The gravitational potential store
Show answer

The thermal store of the brakes The thermal store of the brakes and the surroundings.

Check 28

What is the equation for elastic potential energy?

  1. Ee = k × e
  2. Ee = 0.5 × k × e²
  3. Ee = 0.5 × k × e
Show answer

Ee = 0.5 × k × e² elastic potential energy = 0.5 × spring constant × extension².

Check 29

What is the effect of oil on the moving parts of a machine?

  1. More friction, so the parts move more slowly.
  2. It makes the parts heavier.
  3. Less friction, so less energy is wasted.
Show answer

Less friction, so less energy is wasted. It lubricates them, so there is less friction and less energy is wasted as heat.

Check 30

How does the thermal conductivity of a wall affect how fast a house cools?

  1. Higher conductivity means faster cooling.
  2. Higher conductivity means slower cooling.
  3. Conductivity has no effect on cooling.
Show answer

Higher conductivity means faster cooling. A higher thermal conductivity means energy escapes faster, so the house cools faster.

Check 31

How does the thickness of a wall affect how fast a house cools?

  1. A thicker wall cools faster.
  2. A thicker wall cools more slowly.
  3. The thickness has no effect.
Show answer

A thicker wall cools more slowly. A thicker wall slows the cooling.

Check 32

What is a renewable energy resource?

  1. One that never causes pollution.
  2. One that works all day and night.
  3. One that is replaced as it is used.
Show answer

One that is replaced as it is used. One that is being replaced as it is used, or can be replaced.

Check 33

Name three fossil fuels.

  1. Coal, oil and gas
  2. Wind, solar and tides
  3. Uranium, wood and coal
Show answer

Coal, oil and gas Coal, oil and gas.

Check 34

Why is solar power not reliable?

  1. It uses up a fuel that runs out.
  2. It depends on daylight and weather.
  3. It makes carbon dioxide.
Show answer

It depends on daylight and weather. It only works well in daylight, and cloud reduces it.

Check 35

Give one environmental problem with burning fossil fuels.

  1. It makes radioactive waste.
  2. It floods valleys.
  3. It releases carbon dioxide and adds to global warming.
Show answer

It releases carbon dioxide and adds to global warming. It releases carbon dioxide, which adds to global warming.

Check 36

Give one problem with nuclear power.

  1. It makes radioactive waste.
  2. It releases lots of carbon dioxide.
  3. It only works when the wind blows.
Show answer

It makes radioactive waste. It makes radioactive waste that stays dangerous for a very long time.

Check 37

Why can science not decide which energy resource a country should use?

  1. Science cannot measure the effect of any resource.
  2. The choice also depends on politics, money and ethics.
  3. Every resource has the same effects.
Show answer

The choice also depends on politics, money and ethics. The choice also depends on politics, money, society and ethics.

Check 38

What is a reason for the growth in the use of renewable resources?

Show answer

To reduce carbon dioxide emissions, lower costs of renewables and government policy.

Check 39

How should you describe a trend in energy use?

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Quote figures, say whether they rise or fall, and give a reason.

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