P1: Energy Flashcards
give the equation for kinetic energy. Include units
1/2 mass x (velocity)^2
where:
energy = joules ( J)
mass = kg
velocity= (m/s)
give the equation for elastic potential energy. give units for all quantities/ involved
1/2 x spring constant x (extension)^2
energy: joules (J)
spring constant: (N/M)
extension: (m)
what is the equation for gravity potential energy? give the units for all quantities involved
- mgh
- mass x gravitational field strength x height
energy: joules (J)
mass: kg
g: (N/kg)
height: (m)
define the specific heat capacity of a substance
- the amount of energy needed to raise the temperature of 1 kilogram of a substance by 1 degree Celsius
state the units for specific heat capacity
J/*C/kg
joules/degree Celcius/Kilogram
what is the definition of ‘ Power’?
- the rate at which energy is transferred ( or rate at which work is done)
state two equations for power. Give units for all quantities involved.
power = energy transferred / time
power = work done / time
energy ( J)
work done (J)
Time ( s)
what is the unit of power?
Watt (W)
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.
Motor A
- the energy transferred is the same but the time taken is less ( P=E/t)
Describe the energy changes involved when a ball is thrown upwards and then returns to its starting position , Ignore air resistance.
- Upwards: KE is converted to GPE
- Peak: Maximum GPE , zero Kinetic energy
- Downwards: GPE is converted to KE
Describe the energy transfers for a bungee jumper
- 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.
Explain why a bungee jumper slows down once the cord begins to stretch.
- kinetic energy decreases since its converted to elastic potential energy
- Since KE is proportional to ( velocity)*2 as KE decreases, so does velocity
Explain why the bungee jumper does not return to their original height
- some energy was transferred to the thermal energy store of the surroundings by heating as the rope stretched and then shortened again.
Describe the energy transfers that occur when a moving object hits an obstacle ( e.g a car and a wall)
- 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.
Describe the energy changes that occur in a filament light-bulb
- electrical energy is transferred into light and heat energy
- light is a useful energy form, heat is waste energy
Describe the energy transfer that occurs when an object is accelerated by a constant force
- 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).
state 4 different stores of energy
- kinetic energy
- gravitational potential energy
- elastic potential energy
- Chemical energy
give three examples of chemical energy stores
- food
- fuel ( eg. wood, coal, petrol)
- batteries
State the law of energy conservation
- energy cannot be created or destroyed ( it can only be transferred into different forms)
State any changes in the total energy of a ball that is kicked, assuming that no external forces act.
- the total energy of the system remains constant due to the conservation of energy
what is waste energy?
- energy that is not used by the device for its desired purpose
State two equations to calculate efficiency
useful output energy transfer/ total input energy transfer
useful power output/ total power input
Describe the waste energy transfers that occur when bringing water to a boil in an electric kettle
- Some energy is lost to the heat that warms the kettle itself and some is converted to sound energy
describe the energy transfers that occur when a liquid is heated
- 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
Give two ways the efficiency of a system be increased
- reducing waste output ( by lubrication/thermal insulation)
- recycling waste output (eg recycling thermal waste energy as input energy)
state three methods of reducing heat loss in a building
- double glazing
- loft and wall insulation
- thicker walls
state the result of energy transfer of a material with a high thermal conductivity
- the rate of energy transfer through the material is higher than for a material with a lower thermal conductivity
Do double-glazed windows have a higher or lower thermal conductivity than single-glazed windows?
lower meaning less thermal energy transfers through them
give two factors that affect the rate of cooling of a building
- the thickness of the walls
- the thermal conductivity of the walls
how can the efficiency of a mechanical machine with moving parts be improved?
- lubricate any moving parts to reduce the friction and therefore energy loss due to heating
how can the efficiency of a radiator be improved?
- installing metal foil sheets behind the radiator to reflect the heat back into the room rather than it being absorbed back into the walls
how can the efficiency of boiling water in a pan to be improved.
- by placing a lid on the pan to reduce the heat loss from the top
what is a renewable energy resource?
- an energy source which can be replenished as it is being used up
State three advantages of fossil fuels as an energy resource
- reliable: not dependent on external factors so can generate power anytime
- can produce large amounts of energy for a given quantity
- still relatively abundant, so cost effective
give four examples of renewable energy resources
- Wind energy
- Hydro energy
- Tidal Energy
- Solar Energy
give an example of a non-renewable energy resource
- fossil fuels ( eg coal, oil and gas )
give two advantages of generating power using gas rather than coal?
- Flexible generation: Gas power stations have short start-up times so can be switched on/off more easily
- Lower emissions of carbon dioxide
State two disadvantages of using renewable energy resources to generate power
- 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
Explain two environmental impacts of the burning of fossil fuels
- Carbon dioxide contributes to the greenhouse effect and causes global warming
- sulfur dioxide leads to acid rain which can damage buildings and crops
State three advantages of nuclear power
- produces very large amounts of energy for relatively small quantities of fuel
- Doesn’t release greenhouse gases and so doesnt contribute to climate change
- low fuel costs
State three disadvantages of nuclear power
- Produces nuclear waste which is harmful for humans and must be safely stored for centuries
- a non-renewable energy source
- risk of nuclear accidents , which have fatal consequences on humans and the environment
how does hydroelectric power produce energy?
- 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
Describe the energy transfers that occur when a vehicle is slowing down
- 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.
give 5 disadvantages of using biofuels?
- 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
give three advantages of tidal energy sources
- 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
give two disadvantages of hydroelectric power?
- the dam may cause flooding
- it can cost a lot to install the required infrastructure
give three advantages of solar panels
- 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
give an example of a social factor which may act as a deterrent for certain types of energy production.
- visual pollution
- sound pollution
