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10 - Work,Energy,Power (10.2 Kinetic energy (Potential energy (Energy of…
10 - Work,Energy,Power
10.1 Work and energy
Energy rules
Energy is needed to make stationary objects move, change their shape or warm up. when lifting an object, energy is transferred from the muscles to object
Energy stores- gravitational potential stores, kinetic stores, thermal stores, elastic stores
Energy transfers- radiation, electrically, mechanically
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Forces at work
Work is done on an object when a force makes it move(energy transferred). Amount of work done depends on force and distance object has moved. Greater the force or further the distance, greater the work done
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Force-distance graph
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Stretch the spring to extensionΔL, work done = 1/2FΔL
10.2 Kinetic energy
Kinetic energy
Energy of an object due to motion. Faster the object moves, more kinetic energy it has.
Kinetic energy, Ek = 1/2mv²
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Pendulum bob
Displaced from equilibrium position and then released with thread taut. The bob passes through equilibrium position at max speed slows down to reach max height. If initial height = h0 then whenever above equilibrium position = h. Kinetic energy = loss of potential energy from max height. 1/2mv²=mg(h0-h)
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10.3 Power
Power and energy
Energy can be transferred from object to object by work done,heat transfer, electricity, sound waves and electromagnetic radiation
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Power measurements
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Electrical power
Power of light bulb can be measured by using joulemeter. It is read before and after the bulb is switched on. difference = energy supplied to bulb. If switched on for measured time, power = energy supplied/time taken
Engine power
When a powered object moves at constant velocity at constant height, resistive forces = motive force
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When a powered object gains speed, the output force exceeds the resistive forces on it
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Juggernaut physics
Maximum weight of a truck with six or more axles on UK roads must not exceed 44 tonnes, corresponds to total mass of 44000kg(set to prevent damage). EU regulations limit output power to 6kW per tonne. Maximum output power of 44 tonne truck = 264kW
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