A ball of mass `m` moving with speed `v` towards the right strikes a wall moving towards the left with speed `u`. Find the change in the `K.E.` of the ball if the collision is elastic.

Explanation

To solve the problem of finding the change in kinetic energy of a ball after an elastic collision with a wall, we can follow these steps:

### Step 1: Understand the Initial Conditions
- We have a ball of mass \( m \) moving to the right with speed \( v \).
- The wall is moving to the left with speed \( u \).

### Step 2: Determine the Initial Kinetic Energy of the Ball
The initial kinetic energy \( KE_{initial} \) of the ball can be calculated using the formula:
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