### Elastic Collision

Elastic collision is the collision where the kinetic energy is conserved after the collision.

Total Kinetic Energy before Collision

= Total Kinetic Energy after Collision

Additional notes:

- In an elastic collision, the 2 objects separated right after the collision, and
- the momentum is conserved after the collision.
- Total energy is conserved after the collision.

### Inelastic Collision

Inelastic collision is the collision where the kinetic energy is not conserved after the collision.

Additional notes:

- In a perfectly elastic collision, the 2 objects attach together after the collision, and
- the momentum is also conserved after the collision.
- Total energy is conserved after the collision.

**Example – Perfectly Inelastic Collision**:

A lorry of mass 8000kg is moving with a velocity of 30 ms^{-1}. The lorry is then accidentally collides with a car of mass 1500kg moving in the same direction with a velocity of 20 ms^{-1}. After the collision, both the vehicles attach together and move with a speed of velocity v. Find the value of v.**Answer**:

(IMPORTANT: When 2 object attach together, they move with same speed.)

m_{1} = 8000kg

m_{2} = 1500kg

u_{1} = 30 ms^{-1}

u_{2} = 20 ms^{-1}

v_{1} = v

v_{2} = v

According to the principle of conservation of momentum,

m_{1}u_{1} + m_{2}u_{2} = m_{1}v_{1} + m_{2}v_{2}

(8,000)(30) + (1,500)(20) = (8,000)v+ (1,500)v

270,000 = 9500v

v = 28.42 ms^{-1}

This topic needs to be understood with the help of practical and videos are helpful to understand it.Collisions principle lies in the newton's equation of motion which are basics of Physics.The law of conservation of momentum and energy are used in collision problems.

Instantaneous Speed