# AS Physics Energy

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• Created by: ellie
• Created on: 01-06-13 14:27
• Energy
• Potential
• Kinetic Energy= 1/2mv^2
• Work done to raise an object= force * distance moved in that direction (=mgdeltah). This is its change in gravitational potential energy
• After object falls through a vertical height of deltah,1/2mv^2 is equal to mgdeltah
• Apendulum bob- Kinetic energy = mg(h-h
• Fairground downward track- work done to overcome friction and air resistance= mgh- 1/2mv^2
• Power
• Power is defined as the rate of transfer of energy
• Power= change in work done/ change in time
• Electrical
• The power of a bulb can be measured in a circuit with a joulemeter. The difference in readings before and after the bulb is turned on is the energy supplied to the bulb. Power can be found using this value and the time
• Engine
• Output power of engine can be called its motive power
• At constant height and velocity, the motive force= any resistant forces
• Work done per second= force * distance moved per second
• Output power of engine= P=Fv
• Muscle
• Your gain of potential energy= your weight gain * total height gain
• Your muscle power= weight * height gain/ time taken
• Renewable
• Solar
• A solar cell panel produces electricity directly
• A Solar heating panel can heat water to 70 degrees and can absorb up to 500 J/s of energy on a British Summer day.
• Wind
• Typical modern wind turbine can generate about 2MW of electrical power
• Kinetic energy per second of wind passing through turbine= 1/2pv^3A, where p= denisty of air, v= speed of air and A= area the blades sweep
• Water
• hydroelectric and tidal power stations make use of potential energy released by water when it runs to a lower level
• Hydroelectric power stations release less water per second but from a much higher height than tidal power stations.
• Efficiency
• Work done= Fs= W
• Output Pwer= Fv where F= output force and v= speed of object
• Efficiency of machine= work done by machine/ energy supplied to machine
• Efficiency= output power of machine/ input power of machine
• To find percentage efficiency times by 100
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