# Elastic and Inelastic Collision

### 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

• 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.

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

m1 = 8000kg
m2 = 1500kg
u1 = 30 ms-1
u2 = 20 ms-1
v1 = v
v2 = v

According to the principle of conservation of momentum,

m1u1 + m2u2 = m1v1 + m2v2
(8,000)(30) + (1,500)(20) = (8,000)v+ (1,500)v
270,000 = 9500v
v = 28.42 ms-1