Topic 3 Flashcards
3.5 3.7
3.1
State the equation for GPE
GPE=mgh
3.1
Rearrange the GPE equation to make h the subject
h=GPE/mg
3.1
Rearrange the GPE equation to make g the subject
g=GPE/mh
3.1
Rearrange the GPE equation to make m the subject
m=GPE/gh
3.2
State the equation for KE
1/2m(v²)
3.2
Rearrange the KE equation to make m the subject
m=2KE/v²
3.2
Rearrange the KE equation to make v the subject
v=√2KE/m
3.3
State how energy is transferred in a light bulb
Electrical -> light (useful) & thermal (waste)
3.4
Explain the law of conservation of energy
-E can’t be created or destroyed
-Only stored or transferred
3.5
Describe the energy transfers that take place in a hydroelectric dam
-KE from flowing water -> KE store of turbine -> KE store of generator
-Some dissipated as thermal E
-Transfers electrically to National Grid
3.5
Describe the energy transfers that take place when fossil fuels are burnt for energy (what about nuclear fuels?)
-Chemical store of fuels -> thermal store of water -> KE store of turbine -> KE store of generator
-Electrically to National Grid
-Starts with nuclear energy of fuel, rest same
3.5
Describe the energy changes involved when a ball is projected upwards
Chemical energy from person holding ball -> KE store of ball as moves up -> GPE as h increases
3.5
Describe the energy changes involved when a moving object hits an object. Use a car as an example
-Chemical store in fuel -> KE of car
-KE decrease when hits object
-Most KE dissipates to themal store of surroundings
-Some E transferred mechanically to thermal store of wall (F of car on wall)
-Some dissipated as sound waves
3.5
Describe the energy changes involved when an object is being accelerated by a constant force
Chemical E when stationary -> KE when accelerates
3.5
Describe the energy changes involved when a vehicle is slowing down
-KE when moving
-Dissipated as thermal (due to friction) when decelerates
-Some dissipated as sound waves
3.5
Describe the energy changes involved when water is boiled in an electric kettle
Electrical E from mains supply -> thermal store of heating element in kettle -> thermal store of water
3.5
Describe the energy changes involved when someone is jumping on a trampoline
-KE from jumping person -> EPE of trampoline -> back to KE as bounce up -> GPE as h increases
-Some dissipated to thermal store of surrounding
3.6
When there are energy transfers in a closed system, there is no net change to the total energy. Explain why
-E transfers between stores
-But overall E of system = conserved
3.6
Define the term net change of energy
Overall change to whole system
3.7
When do mechanical processes become wasteful?
-When cause rise in temp
-Dissipated to thermal store of surroundings
3.8
Explain what happens in all system changes
E = dissipated -> stored in less useful ways
3.8
State 4 reasons as to why machines waste energy
-Friction between moving parts
-Air R
-Electrical R
-Noise
3.9/3.12
Explain 2 ways of reducing energy transfers within a system. What does this also do?
Lubrication
-Reduces friction between moving parts
Thermal insulation
Increase efficiency
3.9
How is heat loss from a house reduced by having a cavity wall?
-Air trapped between walls
-Air = bad thermal conductor
