Topic 8 - Energy Forces & Work Flashcards
State the law of energy conservation
Energy cannot be created or destroyed only transferred into different forms
Describe the energy changes involved when a ball is thrown upwards and then returns to its starting position. Ignore air resistance.
Upwards: KE converted to GPE
Peak: Max GPE, zero KE
Downwards: GPE converted to KE
State energy changes in total energy of ball that is kicked, assuming no external forces act
Total energy of system remains constant due to conservation of energy
Describe the energy changes that occur in a filament light bulb
Electrical enegry transferred into light and heat energy
Light is useful energy form, heat is waste energy
Describe energy transfers for a bungee jumper
When falling, GPE converted to KE of jumper
As cord tightens, KE converted and stored as elastic potential energy
At lowest pt, jumpers initial GPE equals the EPE stored in cord
Explain why a bungee jumper slows down once the cord begins to stretch
KE decreases as it converts to EPE
Since KE is proportional to (velocity)², as KE decreases, so does velocity
Describe the energy changes in a power station
Heat energy released in reaction heats water to make steam
Steam moves turbine, converting KE
KE turns generator
Electrical energy as generator generates electricity
In what ways can the energy of a system be changes?
Through work done by forces
Through electrical imput
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
What equation is used to measure the work done on an object
Work done (J) = force (N) x distance (m) W = fd
Why do wasteful mechanical processes cause a rise in the temperature of the surroundings?
They cause energy to be transferred by heating the surroundings
What is the equation for kinetic energy?
E = 1/2 m v²
Energy (J) = 1/2 x Mass (kg) x (Velocity (m/s))²
Whats the equation for gravitational potential energy?
E = mgh
Energy (J) = Mass (kg) x GFS (N/kg) x Height (m)
