Topic 1-Energy changes in a system Flashcards
What is the equation for kinetic energy? Give SI units for all quantities involved.
1/2x mass x velocity^2 ,1/2 mv^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 x Spring constant x (Extension)2, 1/2kx^2, Energy (J), spring constant (N/m), extension (m)
What is the equation for gravity potential energy?
mass x gravitational field strength x height
Define the specific heat capacity of a substance
The amount of energy needed to raise the temperature of 1kg of a substance by 1 degree celsius
State the units for specific heat capacity
J/°C/kg
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 transfer 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 jumpers 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 its converted to elastic potential energy
Since KE is proportional to (velocity)^2, as KE decreases so does velocity
Give example of chemical energy stores
Food
Fuel
Batteries
State the 8 different energy stores
nuclear, chemical, magnetic, gravitational potential, kinetic, thermal, elastic potential and electrostatic. You can use the mnemonic ‘Naomi Campbell Met Grace Kelly To Eat Enchiladads’
