Doing work is the way of transferring energy from one object to another object.

The work done is defined as the product of force and distance moved in the direction of the force.

W=F ×s

Work done = energy transferred.

**Force, distance and direction**

The work done by the force depends on the angle between the force and the distance it moves.

Work done = Fs cosƟ

**Work done by gas**

Gas at pressure p inside a cylinder of cross sectional area A. The cylinder is closed by a moveable piston. The gas pushes the piston a distance s. and force f is applied.

So,

Pressure =force/area

force=pressure ×area

F= p × A

Work done,

W = p × A × s

W = pΔV

**Gravitational potential energy (g.p.e.) = mgh**

**Kinetic Energy (E _{k}) = **

**mv**

^{2}It is given by;

V^{2 }= u^{2} +2as (u=0)

V^{2 }=2as

Multiplying both sides by ½

½ mv^{2} = mas

So, F= ½ mv^{2 }

Efficiency = (useful output energy)/(total input energy) ×100%

**Principle of conservation of energy**

Energy can neither be created nor be destroyed, it can only be transferred from one form to another.

**Power**

Power is defined as the rate of work done. Its unit is watt.

Power=(work done)/(time taken)

P= W/t

Suppose the body is moving with velocity v. It provides the necessary force F in time t, it travels the distance s which is equal to vt. So the work done by it is:

Work done = force × distance

W= F × v × t

P = W/t = (F ×v×t)/t

P= F × v

Power = force × velocity.