P1: Energy

Question 1

give the equation for kinetic energy. Include units

Answer 1

1/2 mass x (velocity)^2
where:
energy = joules ( J)
mass = kg
velocity= (m/s)

Question 2

give the equation for elastic potential energy. give units for all quantities/ involved

Answer 2

1/2 x spring constant x (extension)^2
energy: joules (J)
spring constant: (N/M)
extension: (m)

Question 3

what is the equation for gravity potential energy? give the units for all quantities involved

Answer 3

• mgh
• mass x gravitational field strength x height
  energy: joules (J)
  mass: kg
  g: (N/kg)
  height: (m)

Question 4

define the specific heat capacity of a substance

Answer 4

• the amount of energy needed to raise the temperature of 1 kilogram of a substance by 1 degree Celsius

Question 5

state the units for specific heat capacity

Answer 5

J/*C/kg
joules/degree Celcius/Kilogram

Question 6

what is the definition of ‘ Power’?

Answer 6

• the rate at which energy is transferred ( or rate at which work is done)

Question 7

state two equations for power. Give units for all quantities involved.

Answer 7

power = energy transferred / time
power = work done / time
energy ( J)
work done (J)
Time ( s)

Question 8

what is the unit of power?

Answer 8

Watt (W)

Question 9

Two motor lift the same mass through the same height. Motor A does this in half the time of Moto B. Which dissipates the most power.

Answer 9

Motor A
- the energy transferred is the same but the time taken is less ( P=E/t)

Question 10

Describe the energy changes involved when a ball is thrown upwards and then returns to its starting position , Ignore air resistance.

Answer 10

• Upwards: KE is converted to GPE
• Peak: Maximum GPE , zero Kinetic energy
• Downwards: GPE is converted to KE

Question 11

Describe the energy transfers for a bungee jumper

Answer 11

• When the rope is slack and the person is falling the GPE is converted to KE of jumper
• As the cord tightens, the fall is slower as KE is converted and stored as Elastic Potential energy
• At the bottom, the rope recoils & the energy in the EPE store of the rope decreases and the jumper’s KE store increases until the rope becomes slack
• ,the jumper’s KE store eventually decreases to 0. The jumper’s GPE increases
  throughout the ascent.

Question 12

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

Answer 12

• kinetic energy decreases since its converted to elastic potential energy
• Since KE is proportional to ( velocity)*2 as KE decreases, so does velocity

Question 13

Explain why the bungee jumper does not return to their original height

Answer 13

• some energy was transferred to the thermal energy store of the surroundings by heating as the rope stretched and then shortened again.

Question 14

Describe the energy transfers that occur when a moving object hits an obstacle ( e.g a car and a wall)

Answer 14

• Initially, the car has kinetic energy causing it to move .
• After the collision ,KE is transferred into the thermal store of the car and the wall
• This thermal energy is dispersed into the air and surrounding materials
• Some energy remains in the object’s kinetic store as it moves away after the collision.

Question 15

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

Answer 15

• electrical energy is transferred into light and heat energy
• light is a useful energy form, heat is waste energy

Question 16

Describe the energy transfer that occurs when an object is accelerated by a constant force

Answer 16

• energy is required to accelerate the object either chemical, thermal or electrical (DEPENDENT ON CONTEXT).
• This energy will then be converted into kinetic energy (used to accelerate the object).

Question 17

state 4 different stores of energy

Answer 17

1. kinetic energy
2. gravitational potential energy
3. elastic potential energy
4. Chemical energy

Question 18

give three examples of chemical energy stores

Answer 18

• food
• fuel ( eg. wood, coal, petrol)
• batteries

Question 19

State the law of energy conservation

Answer 19

• energy cannot be created or destroyed ( it can only be transferred into different forms)

Question 20

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

Answer 20

• the total energy of the system remains constant due to the conservation of energy

Question 21

what is waste energy?

Answer 21

• energy that is not used by the device for its desired purpose

Question 22

State two equations to calculate efficiency

Answer 22

useful output energy transfer/ total input energy transfer
useful power output/ total power input

Question 23

Describe the waste energy transfers that occur when bringing water to a boil in an electric kettle

Answer 23

• Some energy is lost to the heat that warms the kettle itself and some is converted to sound energy

Question 24

describe the energy transfers that occur when a liquid is heated

Answer 24

• when power is turned on and a current is flowing, the current in the electric circuit transfers energy to the heater ( does work)
• this transfers electric energy from the power supply to the thermal energy store of the heater
• causing the liquid temperature to increase

Question 25

Give two ways the efficiency of a system be increased

Answer 25

1. reducing waste output ( by lubrication/thermal insulation) 2. recycling waste output (eg recycling thermal waste energy as input energy)

Question 26

state three methods of reducing heat loss in a building

Answer 26

1. double glazing 2. loft and wall insulation 3. thicker walls

Question 27

state the result of energy transfer of a material with a high thermal conductivity

Answer 27

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

Question 28

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

Answer 28

lower meaning less thermal energy transfers through them

Question 29

give two factors that affect the rate of cooling of a building

Answer 29

- the thickness of the walls - the thermal conductivity of the walls

Question 30

how can the efficiency of a mechanical machine with moving parts be improved?

Answer 30

- lubricate any moving parts to reduce the friction and therefore energy loss due to heating

Question 31

how can the efficiency of a radiator be improved?

Answer 31

- installing metal foil sheets behind the radiator to reflect the heat back into the room rather than it being absorbed back into the walls

Question 32

how can the efficiency of boiling water in a pan to be improved.

Answer 32

- by placing a lid on the pan to reduce the heat loss from the top

Question 33

what is a renewable energy resource?

Answer 33

- an energy source which can be replenished as it is being used up

Question 34

State three advantages of fossil fuels as an energy resource

Answer 34

1. reliable: not dependent on external factors so can generate power anytime 2. can produce large amounts of energy for a given quantity 3. still relatively abundant, so cost effective

Question 35

give four examples of renewable energy resources

Answer 35

1. Wind energy 2. Hydro energy 3. Tidal Energy 4. Solar Energy

Question 36

give an example of a non-renewable energy resource

Answer 36

- fossil fuels ( eg coal, oil and gas )

Question 37

give two advantages of generating power using gas rather than coal?

Answer 37

1. Flexible generation: Gas power stations have short start-up times so can be switched on/off more easily 2. Lower emissions of carbon dioxide

Question 38

State two disadvantages of using renewable energy resources to generate power

Answer 38

- output often determined by external factors ( like wind speed) so supply is uncertain - generating power through other means is often more efficient and economically beneficial

Question 39

Explain two environmental impacts of the burning of fossil fuels

Answer 39

- Carbon dioxide contributes to the greenhouse effect and causes global warming - sulfur dioxide leads to acid rain which can damage buildings and crops

Question 40

State three advantages of nuclear power

Answer 40

1. produces very large amounts of energy for relatively small quantities of fuel 2. Doesn't release greenhouse gases and so doesnt contribute to climate change 3. low fuel costs

Question 41

State three disadvantages of nuclear power

Answer 41

1. Produces nuclear waste which is harmful for humans and must be safely stored for centuries 2. a non-renewable energy source 3. risk of nuclear accidents , which have fatal consequences on humans and the environment

Question 42

how does hydroelectric power produce energy?

Answer 42

- 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 43

Describe the energy transfers that occur when a vehicle is slowing down

Answer 43

- When a vehicle brakes, velocity decreases as well as the vehicle’s kinetic energy. - The kinetic energy is transferred into heat energy by the brakes.

Question 44

give 5 disadvantages of using biofuels?

Answer 44

- when plants are burned or decayed they release CO2 - in order to grow biofuels, you need to destroy land which leads to problems : - the land could have been natural habitats - destroying land may involve burning plants growing on it which would release CO2 - growing biofuels reduces the land available for growing food

Question 45

give three advantages of tidal energy sources

Answer 45

- they do not produce greenhouse gases - they are quite reliable, as tides happen twice a day - they are cheap to run as tides are natural so are free

Question 46

give two disadvantages of hydroelectric power?

Answer 46

- the dam may cause flooding - it can cost a lot to install the required infrastructure

Question 47

give three advantages of solar panels

Answer 47

- they dont cause harm to the environment - they are a renewable resource - they can be used in remote areas where other types of energy are less accessible

Question 48

give an example of a social factor which may act as a deterrent for certain types of energy production.

Answer 48

- visual pollution - sound pollution