A body of mass 2 kg makes an elastic collision with another body at rest and continues to move in the original direction with a speed equal to one third of its original speed. Find the mass of the second body.

Explanation

To solve the problem, we will use the principles of conservation of momentum and the coefficient of restitution for elastic collisions. Let's break it down step by step.

### Step 1: Define the Variables
Let:
- Mass of the first body, \( m_1 = 2 \, \text{kg} \)
- Initial velocity of the first body, \( V \)
- Mass of the second body, \( m_2 = M \) (unknown)
- Initial velocity of the second body, \( u_2 = 0 \, \text{m/s} \) (at rest)
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