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Ch-11

Work and Energy

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Work

  • A force should act on an object
  • The object must be displaced.
  • Work done= Force*Displacement=Fs
  • For example-girl pulls a trolley and the trolley moves through a distance. The girl has exerted a force on the trolley and it is displaced. Therefore, work is done.

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Positive and Negative Work

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ENERGY

  • An object having a capability to do work is said to possess energy. The object which does the work loses energy and the object on which the work is done gains energy.
  • The SI unit of energy is Joules
  • Two types of energy are potential energy and kinetic energy.

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Potential Energy

The potential energy possessed by the object is the energy present in it by virtue of its position or configuration.

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Kinetic energy

  • Energy possessed by an object when it is in motion is called its kinetic energy.

For example -falling coconut, a speeding car, a rolling stone, a flying aircraft, flowing water, blowing wind, a running athlete etc. possess kinetic energy.

Ek=1/2mv2

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Law of conservation of energy

According to this law, energy can only be converted from one form to another; it can neither be created or destroyed. The total energy before and after the transformation remains the same. The law of conservation of energy is valid in all situations and for all kinds of transformations.

Mgh +1/2mv2=CONSTANT

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POWER

Power is defined as the rate of doing work or the rate of transfer of energy. If an agent does a work W in time t, then power is

given by:

Power = work/time SI unit is Watt

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