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Work: Work is said to be done if a body gets displaced when a force is applied on it. It is measured by the product of force and displacement of the body along the direction of force.If a body gets displaced by ‘d’ when a force ‘F’ acts on it, then Work ‘W’,

*W = F cosθ×d*where ,θ = angle between force and displacement. Work is a scalar quantity.

__SI unit = joule.__

Energy: Capacity of doing work. It is a scalar quantity.

- SI unit = joule.

Energy developed in a body due to work done on it is called mechanical energy.

__Mechanical energy is of two types:__

#### Potential Energy: Capacity of doing work developed in a body due to its position or configuration is called its Potential Energy.

e.g., Energy of stretched or compressed spring, Energy of water collected at a height, etc.

__PE = m g h__#### Kinetic Energy: Energy possess by a body due to its motion is called Kinetic energy of the body. If a body of mass ‘m’ is moving with speed ‘v’, then kinetic energy of the body

**K.E. = 1/2 (mv)^2**

#### Principle of Conservation of Energy: Energy can neither be created nor can be destroyed. It can only be transformed from one form to another. Hence total energy of the universe always remains constant.

e.g., Solar cell converts solar energy into electrical energy, Tube light converts electrical energy into light energy, Battery converts Chemical energy into electrical energy, and so on.###
__Relation between Momentum and Kinetic energy: __

Let mass ‘m’ of the body be constant. E = Kinetic energy, P = momentum = mv.
E =P^2/2m

Clearly when momentum is doubled, kinetic energy becomes four times.

#### Power: Rate of doing work is called power. i.e., P = W/t

- SI unit = watt, named as a respect to the scientist James Watt
- Watt = joule/sec
- 1 Horse power = 746 watt.

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