Topic 1: Energy Flashcards
What is the equation for kinetic energy?
Ek= 0.5 x m x v^2
kinetic energy = 0.5 x mass x velocity^2 (speed)
what is kinetic energy ?
is the energy stored in moving object
units for kinetic energy
kinetic energy - j
mass - kg
velocity - m/s
What is the equation for elastic potential
energy?
Ee =0.5 x spring constant x extension^2
Ee = 0.5 x k x e^2
units for elastic potential energy
Energy (J)
Spring Constant (N/m)
Extension(m)
What is the equation for gravity potential
energy?
Ep = m x g x h
mass x gfs x height
what is gravitational potential energy
gravitational potential energy is the energy stored in an object due to its position above the earth surface
units for gravity potential energy
energy = j mass = kg gfs = 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.
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 SI
units for all quantities involved.
power = energy transferred/time
power = work done/time
What is the unit of power?
Watt (W)
Two motors lift the same mass through the same
height. Motor A does this in half the time of Motor 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 KE
● Downwards: GPE is converted to KE
Describe the energy transfers for a bungee jumper.
● 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
Explain why a bungee jumper slows down once the
cord begins to stretch.
● Kinetic energy decreases since it is
converted to elastic potential energy
● Since KE is proportional to (velocity)2,
as KE decreases, so does velocity.
Give examples of chemical energy stores.
● Food
● Fuel (eg. wood, coal, petrol)
● Batteries
Specific Heat Capacity
energy = mass × specific heat capacity × temperature change
name the different energy stores
chemical kinetic gravitational potential elastic potential thermal Magnetic electrostatic Nuclear
Examples of energy changes in a system:
An object thrown (projected) upwards
As the ball leaves your hand it has a store of kinetic energy.
At its highest point it has a store of gravitational potential energy (G.P.E).
As you are about to catch it just before it hits your hand it has a
store of kinetic energy.
examples of energy changes in a system:
A vehicle slowing down
the moving lorry has a store of kinetic energy.
At the brakes are applied the kinetic energy store decreases the energy is transferred to the internal (thermal) energy store in the brakes and the brakes get hot.
You will hear a sound when the brakes of the lorry are applied, the energy of the sound is also transferred to the internal energy store of the surroundings.
When the lorry stops its kinetic energy store is zero.
Efficiency - 2 equations
efficiency = useful energy output / total energy input
useful power output /
total power
the law of conservation of energy
energy can be stored, transferred or dissipated - but can not be created or destroyed.
The efficiency of a system can be increased by:
o Reducing waste output (lubrication, thermal insulation, etc.)
o Recycling waste output (e.g. absorbing thermal waste and recycling as input
energy)
Reducing energy waste:
Lubrication
o Oil in a motor
o Reduces friction
o So less energy is lost (as heat) through friction
Reducing energy waste:
Thermal Insulation
o Double Glazing
o Less useful thermal energy lost
so low thermal conductivity
insulation
have low thermal conductivity such as fibreglass in the loft, foam in wall cavities and trapped gases in double glazing.
high thermal conductivity
Houses are often built from brick, concrete, wood and glass.
reducing thermal energy transfer from a house using high or low thermal conductivity
low thermal conductivity
Non-renewable
Fossil Fuels (coal, oil,gas) Nuclear Fuel
Renewable
- Biofuel
- Wind
- Hydro-electricity
- Geothermal
- Tidal
- Solar
- Water waves
in a closed energy system t
there can be transfer of energy but not mass. there is no change to the total energy in the system
double glazed windows
cavity walls have a
low conductivity
so less thermal energy can pass through
What is a renewable energy resource?
An energy source that can be
replenished as it is being used up.
Give four examples of renewable energy
resources.
- Wind Energy
- Hydro-Electricity
- Tidal Energy
- Solar Energy
Give an example of a non-renewable
energy resource.
Fossil fuels (for example coal, oil and
gas).
What are the advantages of generating power using
gas rather than coal?
Lower emissions of carbon dioxide
Flexible Generation: Gas power
stations have short start-up times so
can be switched on/off more readily
State two disadvantages of using
renewable energy resources to generate
power.
factors
(like wind speed), so supply is uncertain
more expensive
Explain the environmental impacts of burning fossil
fuels.
● Carbon Dioxide contributes to the
greenhouse effect, and causes global
warming
● Sulphur Dioxide leads to acid rain, which
can damage buildings and crops
Give two reasons for taking repeat readings in an investigation.
. calculate a mean
• spot anomalies
• reduce the effect of random errors
