A proton moves from a large distance with a speed u m/s directly towards a free proton originally at rest. Find the distance of closest of closest approach for the two protons in terms of mass of proton m and its charge e.

Explanation

To find the distance of closest approach for two protons, we can use the principles of conservation of momentum and conservation of energy. Here’s a step-by-step solution:

### Step 1: Understand the Initial Conditions
- We have two protons: one is moving with speed \( u \) towards the other proton, which is at rest.
- The mass of each proton is \( m \) and the charge is \( e \).
- At a large distance, the potential energy between the protons is zero.

### Step 2: Apply Conservation of Momentum
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