An elevator platform is going up at a speed of `20 m//s` and during its upward motion a small ball of `50 g` mass, falling in downward direction, strikes the platform at speed `5 m//s`. Find the speed with which the ball rebounds.

Explanation

To solve the problem step by step, we will use the concept of the coefficient of restitution and the principles of relative velocity in collisions.

### Step-by-Step Solution:

1. **Identify the Given Data:**
- Mass of the ball, \( m = 50 \, \text{g} = 0.05 \, \text{kg} \) (convert grams to kilograms)
- Speed of the elevator (upward), \( V_e = 20 \, \text{m/s} \)
- Speed of the ball before collision (downward), \( u = 5 \, \text{m/s} \)
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