Topic 8: Energy: Forces doing work Flashcards
What is ‘work done’?
The amount of energy transferred
- It is measured in joules (J)
What is the equation for work done by a force?
Work done = Force x Distance moved in the direction of the force
E = F x d
State the law of energy conservation
Energy can’t be created or destroyed
Describe energy changes when ball is thrown
Going up: KE transfers to GPE
Peak height: GPE max and no KE
Going down: GPE transfers to KE
State changes of the total energy when a ball when kicked, assuming no external forces act.
Total energy of the ball remains constant (Conservation of energy).
Describe energy changes of filament lamp.
Electrical energy transfers to light and thermal energy.
Heat is a waste energy while light is useful energy.
Describe energy transfers of a bungee jumper.
When falling GPE converts to KE.
When cord tightens KE is converted and stored as Elastic potential energy.
At lowest point initial GPE = EPE stored in cord.
Explain why a bungee jumper slows down when cord begins to stretch.
Kinetic energy decreases as converted to EPA.
Kinetic energy is proportional to velocity squared, KE decreases, so does velocity.
Describe energy changes in a power station
Heat energy released in a reaction heats water to make steam
Steam moves turbine around
Kinetic energy turns the generator
Generator generates electrical energy.
What 3 ways can energy of a system be changed.
- Work done
- Electrical input
- Heating
How can energy change through work done by forces
Force that moves object (kinetic energy) causes work done to be done over a distance.
Why do wasteful mechanical processes cause a rise of temperature of surroundings.
They cause energy to be transferred by heating the surroundings.
Equation for work done GPE and KE?
Work done = force x distance
KE = 1/2 x mass x velocity squared
GPE = mass x height x gravitational field strength
Definition of power
Rate of which energy is being transferred. (Rate at which work is done).
2 equations for power.
P = energy transferred / time P = work done / time
