# Energy

The energy of a body is defined as it’s capacity or ability for doing work.

Like work, energy is a scalar quantity having magnitude only but no direction.

It’s dimensional formula is [ML²T⁻²].

It is measured in the same unit as work that is Joule in SI and erg in CGS system.

Energy can exist in various form such as Mechanical Energy (Potential Energy + Kinetic Energy), sound energy, heat energy, light energy etc.

## Kinetic Energy

The energy possessed by a body by virtue of its motion is called Kinetic energy. In other words, the amount of work done i.e a moving object can do before coming to rest is equal to its kinetic energy.

Example:- A bullet fired from a gun can pierce a target due to its kinetic energy.

### Notes

1. Kinetic energy of a body is always positive, it can never be negative.

2. Kinetic energy of a body depends upon the frame of reference.

Example:- Kinetic Energy of a person of mass m sitting in a train moving with velocity v is (1/2*m* v2) in the frame of earth and Kinetic Energy of the same person = 0 in the frame of the train.

#### Measurement Of Kinetic Energy

Let a body is initially at rest and the force F is applied on the body to displace it through ds along the direction of the force, then