Work done by the force is equal to the product of the Force and Displacement of the object in the direction of Force.

**θ**

Work is a Scalar Quantity. Its SI Unit is

**Joule**and CGS Unit is

**erg**.

∴

**1 joule = 10**

^{7}erg

Its dimensional formula is [ML

^{2}T

^{-2}].

**Work done by a force is zero,**if

(

**a**) body is not displaced actually, i.e., s = 0

(

**b**) body is displaced perpendicular to the direction of force, i.e.,

θ = 90°

- Work done by a force is
**positive**if angle between F and s is acute angle. - Work done by a force is
**negative**if angle between F and s is obtuse angle. - Work done by a constant force depends only on the initial and final Positions and not on the actual path followed between initial and final positions.

**Work done in different conditions**

**(i) Work done by a variable force is given by**

W = ∫ F * ds

It is equal to the area under the force-displacement graph along with proper sign.

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**POWER**

The rate of work done by a body is called its power.

**Power = Rate of doing work = Work done / Time taken**

If under a constant force F a body is displaced through a distance in time t, then power=

**P=**

**W / t = F**

**× s / t**

**∴ P = F * v = F v cos θ**

where θ is the smaller angle between F and v.

**Power**is a scalar quantity. Its S1 unit is watt and its dimensional formula is [ML

^{2}T

^{-3}].

Its other units are kilowatt and horse power,

1

**kilowatt**= 1000

**watt**

1

**horse power**= 746

**watt**

**Energy**

Energy of a body is its capacity of doing work.

It is a scalar quantity.

Its S1 unit is joule and CGS unit is erg. Its dimensional formula is [ML3T-3].

There are several types of energies, such as mechanical energy (kinetic energy and potential energy), chemical energy, light energy, heat energy, sound energy, nuclear energy, electric energy etc.