3. Conservation of Energy

Question 1

What is meant by the conservation of energy?

Answer 1

• The total amount of energy in a closed system remains constant.
• Energy cannot be made or destroyed but can change from one form to another.

Question 2

What is a closed system?

Answer 2

No energy (or matter) is transferred in or out of the system, so there is no net change in total energy.

Question 3

Describe the energy changes involved when an object is projected upwards / downwards?

Answer 3

KE transferred to GPE, then vice versa as it falls downwards.

Question 4

Name the eight types of energy store

Answer 4

• Kinetic energy
• Gravitational potential energy (GPE)
• Elastic potential energy
• Electrostatic
• Thermal
• Chemical
• Magnetic
• Nuclear

Question 5

Name the four types of energy transfer

Answer 5

• Mechanical (a force doing work)
• Electrical (work done by moving charges)
• Heating
• Radiation (e.g. light or sound)

Question 6

State any changes in the total energy of a ball that is kicked, assuming that no external forces act.

Answer 6

The total energy of the system remains constant due to the conservation of energy.

Question 7

Describe the energy changes that occur in a filament light-bulb.

Answer 7

• Electrical energy is transferred into light and heat energy.
• Light is a useful energy form, heat is waste energy.

Question 8

Describe the energy transfers for a bungee jumper.

Answer 8

• When falling, the GPE is converted to KE of the jumper.
• As the cord tightens, KE is converted and stored as elastic potential energy (EPE).
• At lowest point, the jumper’s initial GPE equals the EPE stored in the cord.

Question 9

Explain why a bungee jumper slows down once the cord begins to stretch.

Answer 9

• Kinetic energy decreases since it is converted to elastic potential energy.
• Since KE is proportional to (velocity)², as KE decreases, so does velocity.

Question 10

What is waste energy?

Answer 10

The energy that is not used by the device for its desired purpose, or not converted into the desired form.

Question 11

State the consequence for energy transfer of a material with a high thermal conductivity.

Answer 11

The rate of energy transfer through the material is higher than for a material with a lower thermal conductivity.

Question 12

Do double-glazed windows have a higher or lower thermal conductivity than single-glazed windows?

Answer 12

Lower thermal conductivity, meaning less energy transfers through them.

Question 13

State three methods of reducing heat loss in a building.

Answer 13

• Double glazing.
• Loft and wall insulation.
• Thicker walls.

Question 14

How can you reduce unwanted energy transfer in a mechanical system?

Answer 14

Reduce friction by lubricating moving parts.

Question 15

How can the efficiency of a system be increased?

Answer 15

• Reducing waste output (by lubrication, thermal insulation, etc.).
• Recycling waste output (e.g. recycling thermal waste energy as input energy).

Question 16

Give an example of a thermal insulation material.

Answer 16

Cotton wool

Question 17

What are renewable resources?

Answer 17

Energy sources which can be replenished as it is being used up.

Question 18

Give four examples of renewable energy resources.

Answer 18

• Wind energy
• Hydro-electricity
• Tidal energy
• Solar energy

Question 19

Give an example of a non-renewable energy resource.

Answer 19

Fossil fuels (for example coal, oil and gas)

Question 20

What are the advantages of generating power using gas rather than coal?

Answer 20

• Flexible generation - gas power stations have short start-up times so can be switched on/off more readily.
• Lower emissions of carbon dioxide.

Question 21

State two disadvantages of using renewable energy resources to generate power.

Answer 21

• Output often determined by external factors (like wind speed), so supply is uncertain.
• Renewable fuels often produce less energy per kg (so more expensive).

Question 22

Explain the environmental impacts of burning fossil fuels.

Answer 22

• Carbon dioxide contributes to the greenhouse effect, and causes global warming.
• Sulfur dioxide leads to acid rain, which can damage buildings and crops.

Question 23

State three advantages of fossil fuels as an energy resource.

Answer 23

1) Reliable - not dependent on external factors so can generate power anytime.
2) Produce large amounts of energy per kg.
3) Still relatively abundant, so cost-effective.

Question 24

State three advantages of nuclear power.

Answer 24

1) Very large amounts of energy per kg of fuel.
2) No greenhouse gases released, so doesn’t contribute to climate change.
3) Low fuel costs.

Question 25

State three disadvantages of nuclear power.

Answer 25

1) Produces nuclear waste which is harmful to humans and must be safely stored for centuries.
2) Non-renewable energy resource so it will run out.
3) Risk of nuclear accidents, which have fatal consequences on humans and the environment.

Question 26

Give examples of social factors to consider in energy production.

Answer 26

• Visual pollution
• Sound pollution

(both of these are disadvantages of wind farms)

Question 27

How does hydroelectric power (HEP) produce energy?

Answer 27

• Rainwater collects behind a dam.
• When this water is released, it is used to turn a turbine.
• This turbine turns a generator which produces electricity.

Question 28

What are some disadvantages of using biofuels?

Answer 28

• When plants are burned/decay they release carbon dioxide.
• In order to grow biofuels, you need to destroy land:
• Habitat destruction
• Deforestation
• CO₂ released when plants are cleared (for example, if they are burned)
• Growing biofuels reduces the land available for food crops.

Question 29

What are the advantages of tidal energy sources?

Answer 29

• No greenhouse gas emissions.
• Fairly reliable (tides occur twice a day).
• Cheap to run as tides are natural, so cost-free.

Question 30

What are the disadvantages of hydroelectric power?

Answer 30

• The dam may cause flooding.
• It can cost a lot to install the required infrastructure.

Question 31

What are some advantages of solar panels?

Answer 31

• They don’t cause harm to the environment.
• They are a renewable resource (will never run out).
• They can be used in remote areas where other types of energy are less accessible.

Question 32

Did electricity use increase or decrease between 1900 and 2000? Why?

Answer 32

Electricity use increased because:
- Population grew.
- People began to use electricity for more things.

Question 33

Is electricity use increasing or decreasing from 2000 onwards? Why?

Answer 33

Electricity use decreasing because:
- Appliances are more efficient.
- People are more careful with amount of energy use.

Question 34

What are three reasons as to why we’re increasing use of renewable energy resources?

Answer 34

1) Burning fossil fuels is very damaging to environment.
2) We need to learn how to get by without non-renewable resources before they run out.
3) Pressure on governments and companies has led them to introduce renewable energy targets.

Question 35

Describe the energy changes involved when an object is projected up a slope.

Answer 35

KE transferred to GPE (and also to heat if friction is present)

Question 36

Describe the energy changes involved when a moving object is hitting an obstacle.

Answer 36

KE transferred to sound / KE transferred to obstacle if that moves too

Question 37

Describe the energy changes involved when an object is being accelerated by a constant force.

Answer 37

• Object is having work done to it, with it gaining KE.
• Whatever supplies the force is having its energy transferred to KE.

Question 38

Describe the energy changes involved when a vehicle is slowing down.

Answer 38

KE is transferred to heat (through brakes)

Question 39

Describe the energy changes involved when boiling water in a kettle.

Answer 39

Energy transferred electrically from the mains to the thermal energy store of kettle’s heating element. Then energy is transferred by heating to thermal energy store of water.