P1,2,3 Flashcards
What is the equation for kinetic energy? Give SI units for all quantities involved.
1⁄2 m v^2
1⁄2 x Mass x (Velocity)^2
Energy (J), Mass(kg), Velocity(m/s)
What is the equation for elastic potential energy? Give SI units for all quantities involved.
1⁄2 k x^2
1⁄2 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/kg °C
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.
This is because 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
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
State 4 different stores of energy.
- Kinetic Energy
- Gravitational Potential Energy
- Elastic Potential Energy
- Chemical Energy
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?
The energy that is not used by the device for its desired purpose.