- Books Name
- Science Made Easy Science Book

- Publication
- Science Made Easy

- Course
- CBSE Class 9

- Subject
- Science

**Kinetic Energy**

Objects in motion possess energy and can do work. This energy is called Kinetic Energy.

**F** = ma.

Also W = F.s

⇒ From the 2nd equation of motion v^{2}−u^{2}=2as,

⇒ we get s = v^{2}−u^{2} / 2a

Substituting equation for work done by a moving body,

⇒ we get W =m.a * v^{2}−u^{2} / 2a

Or

⇒ Kinetic Energy = K.E= 1/2 mv^{2 }(taking initial velocity u=0)

When two identical bodies are in motion, the body with a higher velocity has more K.E.

**Work-energy theorem**

The work-energy theorem states that the net work done by a moving body can be calculated by finding the change in KE.

⇒ W_{net }= KE_{final}− KE_{initial}

⇒ W_{net }= 1/2 mv^{2}

Factors affecting kinetic energy

- Mass
- Velocity
- Momentum

**Potential Energy**

Energy can get stored in an object when work is done on it.

For example, stretching a rubber string. The energy that is possessed by a body by virtue of its configuration or change in position is known as Potential Energy.

The potential energy of an object at a height.

When an object is raised to a certain height, work is done against gravity to change its position. This energy is stored as Potential Energy.

⇒W = F.s

⇒F = ma

In the case of increasing the height, F = mg

Therefore, W (P.E) = mgh

⇒ ΔPE = mg(h_{final} - h_{initial )}