1.1: Energy Changes in a System Flashcards
What is the equation for kinetic energy? Give units.
1/2m(v2)
Ek = 1/2 * Mass * (Velocity)2
J = 1/2 * kg * m/s
What is the equation for gravitational potential energy?
Give the units.
Ep = mgh
Energy = Mass * Gravitational field strength * Height
J = kg * N/kg * m
Define the “Specific Heat Capacity” of a substance.
The amount of energy needed to raise the temperature of 1 kg of a substance by 1°C
State the units for Specific Heat Capacity
J/°C/kg
Joules/Degrees 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 the units.
Power = Energy transferred / Time Power = Work done / Time
Energy - J
Work done - J
Time- s
Power - 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 in 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, GPE is is converted to KE of jumper
- As the cord tightens, KE is converted and stored as EPE (elastic potential)
- At lowest point, the jumper’s initial GPE equals the EPE stored in the chord
Explain why a bungee jumper slows down once the cord begins to stretch.
- KE decreases since it’s converted to EPE
- Since KE is proportional to (velocity)2, as KE decreases, so does velocity
Give examples of chemical energy stores.
- Food
- Fuel (e.g. wood, coal, petrol)
- Batteries
State 4 different stores of energy
- KE
- GPE
- EPE
- Chemical energy
