P2 - Work, energy and power

Question 1

List the energy stores (8)

Answer 1

Thermal, kinetic, gravitational potential, elastic, chemical, magnetic, electrostatic, nuclear

Question 2

List the energy transfers (5)

Answer 2

Mechanical, electrical, heating, radiation (waves like sound and light)

Question 3

Kinetic energy

Answer 3

The energy an object has because of its motion

Question 4

Gravitational potential energy

Answer 4

Energy an object has due to its position above the surface of the Earth
- and object gains GPE when it is lifted and loses it when it falls

Question 5

Elastic energy

Answer 5

Energy stored in an object that is stretched or compressed

Question 6

Electrostatic energy

Answer 6

Potential energy that results from the interaction of charged particles - due to the force of attraction (or repulsion) between two charges

Question 7

Magnetic energy

Answer 7

Energy from magnets and their surrounding magnetic fields - due to the force of attraction (or repulsion) between two magnets

Question 8

Chemical energy

Answer 8

A form of potential energy that is stored in chemical bonds between atoms.
- found in fuels, foods or batteries

Question 9

Nuclear energy

Answer 9

Energy stored in the nucleus of an atom

Question 10

Thermal energy

Answer 10

Energy a substance has due to its temperature (sometimes known as internal energy)
- sum of the kinetic energy and chemical energy of the particles that make up an object

Question 11

Fusion

Answer 11

Creation of energy by joining the nuclei of two atoms (joining)

Question 12

Fission

Answer 12

The splitting of an atomic nucleus to release energy (splitting)

Question 13

Mechanical energy transfer

Answer 13

Energy transferred via a force acting on a body/object
- e.g. collision

Question 14

Electrical energy transfer

Answer 14

Electrical currents can transfer energy from a power source, delivering it to components within a circuit

Question 15

Heating (energy transfer)

Answer 15

Thermal energy can be transferred by conduction, convection or radiation
- conduction: process by which heat energy is transmitted through collisions between neighbouring atoms or molecules
- convection: occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy

Question 16

Radiation (energy transfer)

Answer 16

Energy transferred by light or sound waves

Question 17

Law of Conservation of Energy

Answer 17

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

Question 18

Closed system

Answer 18

A system in which no energy transfers take place in or out of the energy stores of the system
- total amount of energy stays constant

Question 19

Open system

Answer 19

A system in which matter and energy can enter from or escape to the surroundings

Question 20

How is work done

Answer 20

Whenever any work is done, energy gets transferred (mechanically) from one store to another
- energy transfer (J) = work done (J)

Question 21

Work in directions (equal and opposite)

Answer 21

• If a force acts in the direction that an object is moving, then the object will gain energy (usually in the form of kinetic energy)
• If the force acts in the opposite direction to the movement then the object will lose energy (usually as heat)

Question 22

Gravitational field strength on Earth (and Moon)

Answer 22

The gravitational field strength (g) on the Earth is approximately 10 N/kg
- The gravitational field strength on the surface of the Moon is less than on the EarthThis means it would be easier to lift a mass on the Moon than on the Earth

Question 23

Efficiency

Answer 23

The ratio of the useful energy transferred by the device to the total energy supplied to the device

Question 24

What does high or low efficiency dicate about energy transfers

Answer 24

If a system has high efficiency, this means most of the energy transferred is useful
If a system has low efficiency, this means most of the energy transferred is wasted

Question 25

Power

Answer 25

The rate at which work is done

Question 26

Renewable energy

Answer 26

A resource that has a theoretically unlimited supply and is not depleted when used by humans.

Question 27

Non-renewable energy

Answer 27

A source of energy that has a finite supply capable of being used up completely

Question 28

List the main energy sources (8)

Answer 28

Solar energy Wind Bio-fuel Hydroelectricity Geothermal Tidal Nuclear Fossil fuels

Question 29

Fossil fuels (desc., trans., ren. and adv./disadv.)

Answer 29

Burning fossil fuels produces steam which can turn turbines - chemical energy → thermal energy → kinetic energy → electrical energy **Renewable:** No **ADVANTAGES:** reliable; can produce large amounts of energy on fairly short notice **DISADVANTAGES:** produce significant green house gases and pollution

Question 30

Nuclear energy (desc., trans., ren. and adv./disadv.)

Answer 30

Nuclear fuel is reacted producing heat which creates steam - nuclear energy → thermal energy → kinetic energy → electrical energy **Renewable:** No **ADVANTAGES:** reliable; produces no green house gases pr pollution; a large amount of energy is produced from a small amount of fuel **DISADVANTAGES:** produces dangerous radioactive waste; take thousands of years to decay

Question 31

Bio-fuels (desc., trans., ren. and adv./disadv.)

Answer 31

Plant matter, ethanol or methane can be produced and used as a fuel in place of fossil fuels - chemical energy → thermal energy → electrical energy **Renewable:** Yes **ADVANTAGES:** the carbon dioxide produced by burning the fuel is balanced by the carbon di. absorbed whilst producing is **DISADVANTAGES:** Can take up a lot of land and consume resources that are needed for food production

Question 32

Wind (desc., trans., ren. and adv./disadv.)

Question 33

Hydroelectric energy (desc., trans., ren. and adv./disadv.)

Answer 33

Hydroelectric uses the GPE of water stored in reservoirs to turn turbines which generate electricity - gravitational potential energy → kinetic energy → electrical energy **Renewable:** Yes **ADVANTAGES:** reliable and can produce large amount of energy at short notice; no pollution **DISADVANTAGES:** can involve flooding a large area; destroying important wildlife habitats

Question 34

Tidal energy (desc., trans., ren. and adv./disadv.)

Answer 34

A dam is used to trap seawater at high tide, which can then be released through a turbine generating electricity - kinetic energy → electrical energy **Renewable:** Yes **ADVANTAGES:** the tides are very predictable and large amounts of energy can be produced at small intervals **DISADVANTAGES:** very few suitable locations; can cause environmental harm to estuaries and disrupt shipping

Question 35

Geothermal energy (desc., trans., ren. and adv./disadv.)

Answer 35

Heat from underground can be used to create steam, which spins turbine, producing electricity - thermal energy → kinetic energy → electrical energy **Renewable:** Yes **ADVANTAGES:** reliable; geothermal stations are usually small **DISADVANTAGES:** can result in the release of harmful gases from underground; not many places are suitable

Question 36

Solar energy (desc., trans., ren. and adv./disadv.)

Answer 36

Photovoltaic cells can use light to create electricity or thermal radiation from the sun can be used to warm water passing through black pipes - nuclear energy → light & thermal energy → electrical energy **Renewable:** Yes **ADVANTAGES:** produces no green house gases or pollution; good for producing energy in remote places **DISADVANTAGES:** not reliable (only works when its sunny); solar farms can use up lots of farmland

Question 37

Kinetic energy formula

Answer 37

KE=1/2mv^2 (joules)

Question 38

GPE formula

Answer 38

GPE = mgh (joules)

Question 39

Power formula

Answer 39

P = W/t (watts)

Question 40

Efficiency equation

Answer 40

Efficiency = useful energy output / total energy input (%)

Question 41

Gravity on earth

Answer 41

9.8 m/s^2

Question 42

Change in GPE equation

Answer 42

Change in GPE = mass x gravitational field strength x change in height

Question 43

Work done formula

Answer 43

W = Fs (joules) (s = displacement)

Question 44

Efficience equation (2)

Answer 44

Efficiency = (useful power output / power input) x 100