Define energy stores .

Energy stores refer to the different ways in which energy is stored in objects.

True or False? Energy is measured in units of kilograms.

False. Energy is measured in units of joules (J).

Define a system in physics.

A system is an object or group of objects.

True or False? Magnetic and electrostatic are examples of energy stores used in physics.

True. Magnetic and electrostatic are examples of energy stores used in physics. Other examples include kinetic, gravitational potential, elastic, chemical, nuclear, and thermal.

True or False? Objects have energy in their elastic potential store if they are stretched, squashed or bent.

True. Objects have energy in their elastic potential store if they are stretched, squashed or bent.

True or False? All objects have energy in their thermal store, the hotter the object, the less energy it has in this store.

False. All objects have energy in their thermal store, the hotter the object, the more energy it has in this store.

What is the definition of energy transfer pathways ?

Energy transfer pathways are the ways that energy can be transferred from one energy store to another.

True or False? Energy is transferred only through mechanical pathways.

False. Energy can be transferred through various pathways, including mechanical, electrical, heating, and radiation.

Define mechanical working in terms of energy transfer.

Mechanical work is the transfer pathway when a force is exerted over a distance.

True or False? In a falling object, energy is transferred from its kinetic store to its gravitational potential store.

False. In a falling object, energy is transferred from its gravitational potential store to its kinetic store.

State the four energy transfer pathways used in physics.

The four energy transfer pathways used in physics are: mechanical electrical heating radiation

True or False? An example of energy transfer by heating is a hot chocolate warming up cold hands.

True. An example of energy transfer by heating is a hot chocolate warming up cold hands.

Define kinetic energy .

Kinetic energy is the amount of energy an object has as a result of its mass and speed .

When calculating kinetic energy, remember to ______ the speed before multiplying by half the mass.

When calculating kinetic energy, remember to square the speed before multiplying by half the mass.

True or False? Doubling an object's speed doubles its kinetic energy.

False. Kinetic energy depends on speed squared , so doubling the speed quadruples the kinetic energy.

Define gravitational potential energy .

Gravitational potential energy is the energy possessed by an object due to its height in a gravitational field.

If an object falls, energy is transferred ______ its gravitational potential store.

If an object falls, energy is transferred away from its gravitational potential store.

True or False? An object gains energy in its gravitational potential store as it falls.

False. As an object falls, energy is transferred away from its gravitational potential store (usually to its kinetic store).

What happens to the energy in an object's gravitational potential store as the object is lifted?

Energy is transferred to the object's gravitational potential store as it is lifted.

State the principle of conservation of energy .

Energy cannot be created or destroyed , it can only be transferred from one store to another.

How is energy dissipated to the surroundings?

Energy is dissipated (spread out) to the surroundings by heating and radiation . This energy is often not useful, so it is described as wasted energy.

For a system in which energy is conserved, how are the total energy in, useful energy out, and wasted energy related?

The energy is related by: total energy in = useful energy out + wasted energy

An electric motor has a total energy input of 500 J and a useful energy output of 120 J. Calculate the wasted energy.

Wasted energy = Total energy in − Useful energy out = 500 − 120 = 380 J .

True or False? Given enough time, energy in a closed system can eventually be destroyed.

False. By the principle of conservation of energy , energy can never be created or destroyed, regardless of time — it can only be transferred between stores.

A rollercoaster starts at a raised point and travels down to flat ground. Describe the changes to its energy stores as it does so.

Energy is transferred mechanically from the gravitational potential store to the kinetic store . Some energy is also dissipated to the thermal store of the surroundings, due to friction and sound.

Work is done when an object is moved over a distance by a force applied in the direction of its displacement; the force is said to do work on the object.

True or False? The amount of energy transferred is equal to the work done.

True. The amount of energy transferred (in joules) is equal to the work done (in joules or newton-metres) when any mechanical work is done.

True or False? If a force is applied to an object but the object does not move, work is done on the object.

False. If a force is applied but there is no movement, no work is done .

If a force acts in the opposite direction to an object's motion, what happens to the object's energy?

The object loses energy , which is usually dissipated to the surroundings by heating (for example, due to air resistance).

Power is the rate at which energy is transferred or work is done, measured in watts (W).

True or False? Power is the total amount of energy transferred.

False. Power refers to the rate at which energy is transferred or work is done, not the total amount of energy transferred.

True or False? A car has more power if it does the same amount of work in a longer amount of time.

False. A car has more power if it does the same amount of work in a shorter amount of time.

Define the rate of doing work .

The rate of doing work, or power, refers to the amount of work done or energy transferred per unit time. It is measured in watts (W).

True or False? Power and work done are the same quantities.

False. Power is the rate at which energy is transferred or work is done, work done is the total amount of energy transferred.

True or False? Power is often measured in joules (J).

False. Power is typically measured in watts (W), while energy is measured in joules (J).

Define the efficiency of a system.

Efficiency is the ratio of the useful power or energy output from a system to its total power or energy input; it is a measure of the wasted energy in an energy transfer.

True or False? Efficiency has units.

False. Efficiency is a ratio and therefore a dimensionless quantity that does not have any units.

True or False? If an energy transfer is 65% efficient, then 35% of the energy is wasted.

True. If an energy transfer is 65% efficient, then 35% of the energy is wasted.

What does it mean if a system has a low efficiency ?

Most of the energy transferred by the system is wasted , rather than useful.

What is a renewable energy source ?

A renewable energy source is one that is infinite and will not run out.

What is a non-renewable energy source ?

A non-renewable energy source is one that is finite and will run out.

Name two non-renewable energy sources.

Non-renewable energy sources include: Fossil fuels (e.g. gas, oil, coal) Nuclear fuel

Name three renewable energy sources.

Renewable energy sources include: Hydroelectric Waves/tides Wind Solar Geothermal Biofuels

True or False? Once set up, all renewable energy resources produce no greenhouse gas emissions at all.

False. All renewable resources produce no greenhouse gases once set up except biofiels ; greenhouse gases may also be emitted during the production, construction and transport of the equipment.

Burning fossil fuels releases greenhouse gases, which contribute to ______ , and sulphur dioxide, which causes ______ .

Burning fossil fuels releases greenhouse gases, which contribute to global warming , and sulphur dioxide, which causes acid rain .

Give one reason why countries are increasingly using renewable energy resources.

Supplies of fossil fuels are finite and will not last forever, and using non-renewable fuels damages the environment (for example through greenhouse gas emissions and habitat destruction), so more sustainable energy sources are needed.

What is a solar cell ?

A solar cell (photovoltaic cell) transfers energy from sunlight electrically to produce a current, generating electricity . Solar cells are made of semiconducting materials .

Which three energy resources do not come from the Sun?

Geothermal (heat from the Earth's core), nuclear (elements in the Earth's crust) and tidal (mainly the gravitational attraction of the Moon).

How is solar energy transferred to the Earth?

Solar energy is transferred to the Earth by radiation , in the form of visible light and infrared radiation.

What is the difference between a solar cell and a solar panel?

A solar cell transfers energy from sunlight electrically to generate electricity. A solar panel transfers energy from sunlight to the thermal store of water, heating it for domestic use.

What are the main advantages of solar energy?

Advantages of solar energy include: It is a renewable energy source It is highly reliable in hot climates It produces no greenhouse gases or pollution It can be used in remote areas

O LevelPhysicsCambridge (CIE)Flashcards1. Motion, Forces & Energy1.7 Energy, Work & Power

1.7 Energy, Work & Power (Cambridge (CIE) O Level Physics): Flashcards

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Define energy stores.

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Cards in this collection (95)

Define energy stores.
Energy stores refer to the different ways in which energy is stored in objects.
True or False?
Energy is measured in units of kilograms.
False.
Energy is measured in units of joules (J).
Define a system in physics.
A system is an object or group of objects.
True or False?
Magnetic and electrostatic are examples of energy stores used in physics.
True.
Magnetic and electrostatic are examples of energy stores used in physics. Other examples include kinetic, gravitational potential, elastic, chemical, nuclear, and thermal.
True or False?
Objects have energy in their elastic potential store if they are stretched, squashed or bent.
True.
Objects have energy in their elastic potential store if they are stretched, squashed or bent.
True or False?
All objects have energy in their thermal store, the hotter the object, the less energy it has in this store.
False.
All objects have energy in their thermal store, the hotter the object, the more energy it has in this store.
What is the definition of energy transfer pathways?
Energy transfer pathways are the ways that energy can be transferred from one energy store to another.
True or False?
Energy is transferred only through mechanical pathways.
False.
Energy can be transferred through various pathways, including mechanical, electrical, heating, and radiation.
Define mechanical working in terms of energy transfer.
Mechanical work is the transfer pathway when a force is exerted over a distance.
True or False?
In a falling object, energy is transferred from its kinetic store to its gravitational potential store.
False.
In a falling object, energy is transferred from its gravitational potential store to its kinetic store.
State the four energy transfer pathways used in physics.
The four energy transfer pathways used in physics are:
- mechanical
- electrical
- heating
- radiation
True or False?
An example of energy transfer by heating is a hot chocolate warming up cold hands.
True.
An example of energy transfer by heating is a hot chocolate warming up cold hands.
Define kinetic energy.
Kinetic energy is the amount of energy an object has as a result of its mass and speed.
What is the equation for calculating kinetic energy?
The equation for calculating kinetic energy is $E_{k} = \frac{1}{2} m v^{2}$
Where:
- $E_{k}$ = kinetic energy, measured in joules (J)
- $m$ = mass, measured in kilograms (kg)
- $v$ = velocity, measured in metres per second (m/s)
When calculating kinetic energy, remember to ______ the speed before multiplying by half the mass.
When calculating kinetic energy, remember to square the speed before multiplying by half the mass.
What is the kinetic energy of a 2 kg object moving at 4 m/s?
$E_{k} = \frac{1}{2} \times 2 \times 4^{2} = 16 J$
True or False?
Doubling an object's speed doubles its kinetic energy.
False.
Kinetic energy depends on speed squared, so doubling the speed quadruples the kinetic energy.
True or False?
A stationary object has energy in its kinetic energy store.
False.
Kinetic energy depends on speed (v); since a stationary object has a speed of zero, $E_{k} = \frac{1}{2} m (0)^{2} = 0$ .
Define gravitational potential energy.
Gravitational potential energy is the energy possessed by an object due to its height in a gravitational field.
What is the equation for calculating the change in gravitational potential energy?
The equation for calculating gravitational potential energy is $∆ E_{p} = m g ∆ h$
Where:
- $∆ E_{p}$ = change in gravitational potential energy
- $m$ = mass, measured in kilograms (kg)
- $g$ = gravitational field strength, measured in newtons per kilogram (N/kg)
- $∆ h$ = change in height in metres (m)
If an object falls, energy is transferred ______ its gravitational potential store.
If an object falls, energy is transferred away from its gravitational potential store.
What is the change in gravitational potential energy when a 5 kg object is raised by 2 m? Use g = 9.8 N/kg
$∆ E_{p} = 5 \times 9.8 \times 2 = 98 J$
True or False?
An object gains energy in its gravitational potential store as it falls.
False.
As an object falls, energy is transferred away from its gravitational potential store (usually to its kinetic store).
What happens to the energy in an object's gravitational potential store as the object is lifted?
Energy is transferred to the object's gravitational potential store as it is lifted.
State the principle of conservation of energy.
Energy cannot be created or destroyed, it can only be transferred from one store to another.
How is energy dissipated to the surroundings?
Energy is dissipated (spread out) to the surroundings by heating and radiation. This energy is often not useful, so it is described as wasted energy.
For a system in which energy is conserved, how are the total energy in, useful energy out, and wasted energy related?
The energy is related by:
total energy in = useful energy out + wasted energy
An electric motor has a total energy input of 500 J and a useful energy output of 120 J. Calculate the wasted energy.
Wasted energy = Total energy in − Useful energy out = 500 − 120 = 380 J.
True or False?
Given enough time, energy in a closed system can eventually be destroyed.
False.
By the principle of conservation of energy, energy can never be created or destroyed, regardless of time — it can only be transferred between stores.
A rollercoaster starts at a raised point and travels down to flat ground. Describe the changes to its energy stores as it does so.
Energy is transferred mechanically from the gravitational potential store to the kinetic store. Some energy is also dissipated to the thermal store of the surroundings, due to friction and sound.
Define work done.
Work is done when an object is moved over a distance by a force applied in the direction of its displacement; the force is said to do work on the object.
What is the equation for work done?
$W = F \times d$
Where:
- $W$ = work done, measured in joules (J) or newton metres (Nm)
- $F$ = force, measured in newtons (N)
- $d$ = distance, measured in metres (m)
True or False?
The amount of energy transferred is equal to the work done.
True.
The amount of energy transferred (in joules) is equal to the work done (in joules or newton-metres) when any mechanical work is done.
A car's brakes apply a force of 500 N, bringing the car to a stop after 23 m. Calculate the work done by the brakes.
$W = 500 \times 23 = 11 500 J$
True or False?
If a force is applied to an object but the object does not move, work is done on the object.
False.
If a force is applied but there is no movement, no work is done.
If a force acts in the opposite direction to an object's motion, what happens to the object's energy?
The object loses energy, which is usually dissipated to the surroundings by heating (for example, due to air resistance).
Define power.
Power is the rate at which energy is transferred or work is done, measured in watts (W).
True or False?
Power is the total amount of energy transferred.
False.
Power refers to the rate at which energy is transferred or work is done, not the total amount of energy transferred.
True or False?
A car has more power if it does the same amount of work in a longer amount of time.
False.
A car has more power if it does the same amount of work in a shorter amount of time.
What is the formula for calculating power?
The formula for calculating power is:
$P = \frac{W}{t}$ or $P = \frac{Δ E}{t}$
Where:
- $P$ = power, measured in watts (W)
- $W$ = work done, measured in joules (J)
- $Δ E$ = energy transferred, measured in joules (J)
- $t$ = time, measured in seconds (s)
Define the rate of doing work.
The rate of doing work, or power, refers to the amount of work done or energy transferred per unit time. It is measured in watts (W).
True or False?
Power and work done are the same quantities.
False.
Power is the rate at which energy is transferred or work is done, work done is the total amount of energy transferred.
State the equation for calculating energy transferred using power.
The formula for calculating energy transferred using power is:
$∆ E = P \times t$
Where:
- $∆ E$ = $W$ = work done or energy transferred, measured in joules (J)
- $P$ = power, measured in watts (W)
- $t$ = time, measured in seconds (s)
True or False?
Power is often measured in joules (J).
False.
Power is typically measured in watts (W), while energy is measured in joules (J).
Define the efficiency of a system.
Efficiency is the ratio of the useful power or energy output from a system to its total power or energy input; it is a measure of the wasted energy in an energy transfer.
How is efficiency calculated?
Efficiency is calculated as the ratio of useful power or energy output to total power or energy input, usually expressed as a percentage.
$efficiency = \frac{useful energy output}{total energy input} \times 100 %$
True or False?
Efficiency has units.
False.
Efficiency is a ratio and therefore a dimensionless quantity that does not have any units.
An electric motor has an efficiency of 35% and a useful power output of 280 W. Calculate the total power input.
$total power input = \frac{280}{0.35} = 800 W$
True or False?
If an energy transfer is 65% efficient, then 35% of the energy is wasted.
True.
If an energy transfer is 65% efficient, then 35% of the energy is wasted.
What does it mean if a system has a low efficiency?
Most of the energy transferred by the system is wasted, rather than useful.
What is a renewable energy source?
A renewable energy source is one that is infinite and will not run out.
What is a non-renewable energy source?
A non-renewable energy source is one that is finite and will run out.
Name two non-renewable energy sources.
Non-renewable energy sources include:
- Fossil fuels (e.g. gas, oil, coal)
- Nuclear fuel
Name three renewable energy sources.
Renewable energy sources include:
- Hydroelectric
- Waves/tides
- Wind
- Solar
- Geothermal
- Biofuels
True or False?
Once set up, all renewable energy resources produce no greenhouse gas emissions at all.
False.
All renewable resources produce no greenhouse gases once set up except biofiels; greenhouse gases may also be emitted during the production, construction and transport of the equipment.
Burning fossil fuels releases greenhouse gases, which contribute to ______, and sulphur dioxide, which causes ______.
Burning fossil fuels releases greenhouse gases, which contribute to global warming, and sulphur dioxide, which causes acid rain.
Give one reason why countries are increasingly using renewable energy resources.
Supplies of fossil fuels are finite and will not last forever, and using non-renewable fuels damages the environment (for example through greenhouse gas emissions and habitat destruction), so more sustainable energy sources are needed.
What is a solar cell?
A solar cell (photovoltaic cell) transfers energy from sunlight electrically to produce a current, generating electricity. Solar cells are made of semiconducting materials.
Which three energy resources do not come from the Sun?
Geothermal (heat from the Earth's core), nuclear (elements in the Earth's crust) and tidal (mainly the gravitational attraction of the Moon).
How is solar energy transferred to the Earth?
Solar energy is transferred to the Earth by radiation, in the form of visible light and infrared radiation.
What is the difference between a solar cell and a solar panel?
A solar cell transfers energy from sunlight electrically to generate electricity.
A solar panel transfers energy from sunlight to the thermal store of water, heating it for domestic use.
What are the main advantages of solar energy?
Advantages of solar energy include:
- It is a renewable energy source
- It is highly reliable in hot climates
- It produces no greenhouse gases or pollution
- It can be used in remote areas
True or False?
Solar panels produce greenhouse gases and pollution.
False.
Solar panels produce no greenhouse gases or pollution once they are operating.
How do solar furnaces generate electricity?
Solar furnaces consist of large curved mirrors that focus sunlight onto a small area, which heats water to produce steam, which then turns turbines, which generate electricity.
What are fossil fuels?
Fossil fuels are natural resources formed over millions of years from the remains of plants and animals.
What are the three main fossil fuels?
The three main fossil fuels are:
- coal
- oil
- natural gas (methane)
True or False?
Burning fossil fuels produces only carbon dioxide.
False.
Burning fossil fuels produces carbon dioxide which is a greenhouse gas that contributes to global warming. But other harmful gases are also released in the combustion of fossil fuels, such as sulphur dioxide which causes acid rain.
What is a disadvantage of using fossil fuels?
The disadvantages of using fossil fuels include:
- non-renewable (so will run out)
- produce carbon dioxide which contributes to global warming
- produce sulphur dioxide which causes acid rain
What are the main uses of fossil fuels?
The main uses of fossil fuels are transportation, electricity generation, and heating in homes and industries.
True or False?
It takes millions of years for fossil fuels to form.
True.
It takes millions of years for fossil fuels to form. This is why they are considered a non-renewable energy resource.
What energy store is energy transferred from in the combustion of fossil fuels?
Energy is transferred from the chemical store of the fossil fuel during combustion. This energy originally came from sunlight and was transferred to plants and animals through photosynthesis.
How are biofuels produced?
Biofuels are produced from plant matter, such as crops, which undergo processes like fermentation or distillation to extract ethanol or methane for use as alternative fuels to fossil fuels.
What are the main advantage of using biofuels?
The main advantages of biofuels are:
- renewable
- carbon neutral
True or False?
Nuclear power stations release no pollution into the atmosphere during normal operation.
True.
Nuclear power stations do not release pollution into the atmosphere during normal operation.
What is nuclear fuel?
Nuclear fuel refers to materials, such as uranium, used in nuclear reactors to release energy in nuclear fission reactions.
What is the process by which nuclear power stations generate electricity?
Nuclear power stations generate electricity by using the energy released in nuclear fission reactions to heat water to produce steam. The steam then turns turbines connected to generators, which produce electricity.
Why is nuclear fuel a non-renewable resource?
Nuclear fuel is a non-renewable resource because there is a finite supply of uranium ore found in the ground.
How does a hydroelectric dam generate electricity?
Water stored above ground level has energy in its gravitational potential store. As it flows down the slope, this energy transfers to its kinetic energy store, and the flowing water turns a turbine to generate electricity.
What is the main advantage of hydroelectric power?
The main advantage of hydroelectric power is that it can respond to increased electricity demand quickly and reliably.
What is the main disadvantage of building a hydroelectric dam?
The main disadvantage of building a hydroelectric dam is that it requires valleys to be flooded. This results in the destruction of habitats, towns, and villages.
What is wave power?
Wave power uses the rise and fall of waves to turn underwater turbines and generate electricity.
What is tidal power?
Tidal power uses the rise and fall of the tide, often via a tidal barrage, to turn turbines and generate electricity.
How do wave and tidal power stations generate electricity?
Wave and tidal power stations generate electricity by utilising the motion of waves or tides to turn turbines, which then generate electricity through electromagnetic induction.
Give one advantage and one disadvantage of wave and tidal power.
Advantage:
- Renewable energy source
- Produces no pollution
- Highly reliable
- Can produce a large amount of electricity at short notice
Disadvantage:
- Expensive
- Not many suitable locations
- Causes damage to fragile habitats
- Only suitable for small-scale electricity production
What is geothermal energy?
Geothermal energy is energy stored in the thermal store of rocks beneath the Earth's surface from tectonic heating. The hot rocks are used to heat water that can be used as a hot water supply and to produce steam to turn turbines for electricity generation.
True or False?
Geothermal energy is a non-renewable resource.
False.
Geothermal energy is considered a renewable resource.
What is the main advantage of geothermal energy?
The main advantage of geothermal energy is its reliability and renewability. It offers a consistent source of heating and electricity production.
What is the main disadvantage of geothermal energy?
The main disadvantage of geothermal energy is the limited availability of suitable locations for large-scale electricity production.
How does geothermal energy generate electricity?
Geothermal energy generates electricity by heating water and generating steam using the hot rocks beneath the Earth's surface, which drives turbines to produce electricity.
What type of energy resource is geothermal energy?
Geothermal energy is a renewable energy resource. This means it can be replenished naturally and is sustainable over the long term.
What is a wind farm?
A wind farm is a group of wind turbines, often placed in coastal or other windy areas, used to generate electricity for nearby towns and cities.
How do wind turbines generate electricity?
When the wind blows, energy from the kinetic energy store of the wind is mechanically transferred to the kinetic energy store of the turbine blades. This drives the generator to produce electricity.
True or False?
Wind power provides a consistent, reliable supply of electricity.
False.
Wind power only generates electricity when it is windy, so the supply is not consistent.
Give one advantage of wind power.
Advantages of wind power:
- Renewable energy resource
- No fuel costs
- No harmful polluting gases are produced
Give one disadvantage of wind power.
Disadvantages of wind power:
- Can be unreliable (no wind = no electricity production)
- Some consider wind turbines to be visually unappealing
- Can harm wildlife, such as birds

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