topic 1 : energy Flashcards
(43 cards)
what is the equation for kinetic energy give si units for all quantities involved ?
EK = 1/2 mv ( squared)
kinetic energy= 1/2 mass x velocity (squared)
enrgy (j) mass(kg) velocity (m/s)
what is the equation for elastic potential energy, give si units for all quantities involved ?
Ee = 1/2 k e (squared)
elastic potential energy= 1/2 spring constant x ( extension squared)
energy (j) spring constant(n/m) extension (m)
what is the equation for gravitational potential energy ,? give si units for all quantities involved
Ep=mgh
gravitational potential energy= mass x gravitational field strength x height
energy(j) mass(kg) gravitational fieldstrength (n/kg) height(m)
define the “ specific heat capacity “ of a substance
the amount of energy required to raise the temperature of 1kg of a substance by 1 degrees
state the units for specific heat capacity
j/ degrees celcius / kilo gram (kg)
what is the definition of power ?
the rate at which energy is transffered
the rate at which work is done
state two equations for power give si units for all quantities involved
power= energy transfered / 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 transffered 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 kinetic too gpe
peack maximum gpe no kinetic energy
downwards gpe too kinetic
describe the enrgy transfers for a bungee jumper
> falling gpe too Ke >chord tightens Ke too Epe > rope fully stretched zero kinetic too all energy in elastic store > rope recoils elastic too kinetic > during ascent kinetic too gpe > top of ascent all energy in gpe store
explain why the bungee jumper slows down once the chord begins to stretch
> kinetic energy decreases since its converted to elastic potential energy
since Ke is proportional to ( velocity squared ) as the kinetic energy decreases so does speed
the bungee jumper never returns back to its original position , why is that ?
energy is dissipated as thermal energy
> friction with the air particles
> stretching effects in the bungee rope ( which is not full elastic)
give examples of chemical energy stores
food, fuel ( wood coal petrol), batteries
state four different stores of energy
1 kinetic energy
2 gravitational potential energy
3 elastic potential energy
4 chemical energy
state the law of conservation of energy
energy can be transffered usefully, stored or dissipated but cant be created or destroyed
state any changes in the total enrgy of a ball that is kicked assuming that no eternal forces act
the total energy of the system remains constant due to the conservation of energy
what is waste energy ?
the energy that is not used by the device for its desired purpose
describe the energy changes that occur in a filament light bulb
> electrical energy too light + thermal energy
> light energy is the useful energy form , thermal is wasted
state two equations to calculate efficiency
1 useful output energy transfer/ total input energy transfer
2 useful power output / total power input
how can the efficiency of a system be increase ?
1 reducing watse output ( lubrication or thermal insulation)
2 recycling waste output ( recycling thermal waste energy as input energy )
state the consequence for 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 reducing energy transfers through them
what key factors effect the rate of cooling of a building ?
> the thickness of the walls
> the thermal conductivity of the walls
