Assume a proton is a sphere of radius `R~~1` fm. Two protons are fired at each other with the same kinetic energy. K
a. What must K be if the paticles are brought to rest by their mutual Coulomb repulsion when they are just touching each other? We can take this value of K as a representative measure of the height of the Colulomb barrier.

Explanation

To solve the problem, we need to determine the kinetic energy \( K \) required for two protons to come to rest due to their mutual Coulomb repulsion when they are just touching each other. Here’s a step-by-step solution:

### Step 1: Understand the scenario
Two protons are fired at each other with the same kinetic energy \( K \). When they touch, they come to rest due to the repulsive electrostatic force between them.

### Step 2: Apply conservation of energy
The total initial kinetic energy of the system is equal to the total potential energy at the point of contact (when they come to rest). The conservation of energy can be expressed as:
\[
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