Topic 3 - Conservation Of Energy

Question 1

What does conservation of energy mean?

Answer 1

Energy is never created or destroyed. It can be stored, transferred between stores and dissipated but never created or destroyed.

Question 2

How can energy be transferred between stores mechanically?

Answer 2

A force acting on an object and doing work eg pushing

Question 3

How can energy be transferred between stores electrically?

Answer 3

A charge doing work eg charges moving around a circuit

Question 4

How can energy be transferred between stores by heating?

Answer 4

Energy transferred from a hotel object to a colder object eg heating pan on hob

Question 5

How can energy be transferred between stores by radiation?

Answer 5

Energy transferred by waves eg energy from the sun reaching earth by light.

Question 6

Explain what happens in the energy transfer of a ball rolling up a slope

Answer 6

Ball does work against the gravitational force so energy is transferred mechanically from ball kinetic energy store to its GPE store

Question 7

Explain what happens in the energy transfer of a bat hitting a ball

Answer 7

Bat has energy in its KE store. Some is transferred mechanically to the ball’s KE store. Some energy transferred mechanically to the thermal energy stores of bat + ball. Rest carried away by sound.

Question 8

Explain what happens in the energy transfer of a rock dropped from a cliff

Answer 8

Assuming no air resistance, gravity does work on rock so rock constantly accelerates towards ground. Energy is transferred mechanically from rocks GPE store to its KE store.

Question 9

Explain what happens in the energy transfer of a car slowing down without breaking

Answer 9

Energy in KE store of car is transferred mechanically (due to friction) and then by heating to the thermal energy stores of car and road

Question 10

Explain what happens in the energy transfer of a kettle boiling water

Answer 10

Energy transferred electrically from mains to heating element of kettle + then by heating to thermal energy store of water.

Question 11

What is the equation for kinetic energy?

Answer 11

KE (J) = 0.5 x m(kg) x v2(m/s)

Question 12

What is a closed system?

Answer 12

A system (collection of objects) that can be treated completely on its own without any energy being exchanged to or from the surroundings.

Question 13

What happens in a closed system?

Answer 13

When there are energy transfers in a closed system there is no net change to the total energy in that system.

Question 14

When are energy transfers useful?

Answer 14

Energy is only useful when it’s transferred from one store to a useful store.

Question 15

Explain how mechanical processes become wasteful

Answer 15

They become wasteful when they cause a rise in temperature so dissipating energy in heating the surroundings

Question 16

How does lubrication reduce unwanted energy transfers?

Answer 16

For objects touching each other lubricants are used to reduce the friction between the objects’ surfaces when they move. Eg oil.

Question 17

How does insulation reduce unwanted energy transfers?

Answer 17

Thicker walls, cavity walls and insulation decreases the rate of energy transfer through them and reduces the amount of energy transferred by conduction.

Question 18

Are devices 100% efficient? (Eg electric motor)

Answer 18

No device is 100% efficient. Eg 100J supplied to motor, 80J of energy transferred is useful and 20J energy wasted from thermal

Question 19

What are the effects of having lower thermal conductivity walls?

Answer 19

The slower the rate of energy transfer through them meaning the building will cool slower

Question 20

What are the effects of a building having thicker walls?

Answer 20

The thicker the wall the slower the rate of energy transfer so building will cool down slower

Question 21

What is the equation for efficiency?

Answer 21

Efficiency=useful energy transferred(J)/

Total energy supplied to device (J)

Question 22

How can efficiency be increased?

Answer 22

Lubrication and thermal insulation

Question 23

What are the main energy sources available for use on earth?

Answer 23

Bio fuels
Wind
Solar
Hydro electricity 
Fossil fuels
Nuclear fuel
Tides

Question 24

What are fossil fuels?

Answer 24

Coal, oil, gas. Non renewable energy. Natural resources that form underground over millions of years and are burnt to provide energy.

Question 25

Advantages of non renewable energy

Answer 25

Eg fossil fuels and nuclear energy. They can respond quickly to changes in energy demand. Cost to extract fossil fuels is low.

Question 26

Disadvantages of non renewable energy

Answer 26

Produce lots of CO2 which contributes to global warming. Burning coal and oil releases sulfur dioxide which causes acid rain. Oil spillages affect animals that live in and around the sea.