A `10kg` ball and a `20kg` ball approach each other with velocities `20m//s` and `10m//s` respectively. What are their velocities after collision, if the collision is perfectly elastic ?

Explanation

To solve the problem of two balls colliding elastically, we will follow these steps:

### Step 1: Define the Variables
Let:
- \( m_1 = 10 \, \text{kg} \) (mass of the first ball)
- \( m_2 = 20 \, \text{kg} \) (mass of the second ball)
- \( u_1 = 20 \, \text{m/s} \) (initial velocity of the first ball, moving towards the second)
- \( u_2 = -10 \, \text{m/s} \) (initial velocity of the second ball, moving towards the first)
...