Topic 8 - Energy: Forces Doing Work Flashcards
State the law of energy conversation
Energy cannot be created or destroyed it can only be transferred into different forms/other stores
Describe the enegy changed when a ball is thrown up and returns to its starting point. Ignore air resistance
Upwards: KE is transferred to GPE
Peak: Maximum GPE zero KE
Downards: GPE is transferred to KE
State any changes in the total energy of a ball that is kicked - assuminh no external forces act
The total energy of the system remains constant due to conversation of energy.
Describe energy changes that occur in a filament light-bulb
Potential difference is carried by electricity into light and heat energy.
Light is a useful form, heat is waste energy.
Describe energy transfers for a bungee jumper
Falling: GPE is transferred to KE of the jumper
As cord tightens: KE is transferred and stored as EPE
At lowest point: Jumper’s initial GPE equals the EPE stored in the cord
Explain why a bungee jumper slows down once the cord begins to stretch
KE decreases since it is transferred to EPE
Since KE is 1/2mv^2, as KE decreases so does velocity
Describe the energy changes in a power station
Heat energy released in the reaction heats water to make steam
Steam moves the turbine, transferred into KE
KE turns the generator
P.d is then transferred by electricity as the generator turns to the device
What ways can the energy of a system be changed?
Through work done by forces
Through electrical input
Through heating
How can energy be changed through work done by forces?
A force which moves an object (KE) causes work to be done over a distance
Work done equation
Work done = force x distance
J = N x M
Why do wasteful mechanical processes cause a rise in the temperature of the surroundings?
They cause energy to be transferred by heating the surroundings
Kinetic equation
E =1/2mv^2
m = kg
v=m/s
E = J
GPE equation
Energy = mass x gravitational field strength x height Mass = kg Gfs = N/Kg Height = m
What is the definition of power?
The rate at which enery is transferred (or rate at which work is done).
Power Equation
Power = work done / time Power = energy transferred/time Energy and Work done = J time = S Power = W
