Energy changes in a system Flashcards
What is the equation for elastic potential
energy? Give SI units for all quantities
involved.
½ k x2
½ x Spring Constant x (Extension)²
Energy (J), Spring Constant (N/m), Extension(m)
What is the equation for gravity potential
energy? Give SI units for all quantities
involved.
mgh
Mass x Gravitational Field Strength x Height
Energy (J), Mass(kg), Gravitational Field Strength (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 Celsius/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 SI
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 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
KE (Kinetic Energy), GPE (Gravitational Potential Energy
Describe the energy transfers for a
bungee jumper.
● When falling, the GPE is converted to KE of
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
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Explain why a bungee jumper slow
Give examples of chemical energy
stores.
● Food
● Fuel (eg. wood, coal, petrol)
● Batteries
State 4 different stores of energy.
- Kinetic Energy
- Gravitational Potential Energy
- Elastic Potential Energy
- Chemical Energy
