## Distance Of Closest Approach

1. The problem statement, all variables and given/known data

Two Protons are moving directly toward one another. When they are very far apart, their initial speeds are 2.1 x 10^6 m/s. What is the distance of closest approach?

2. Relevant equations

3. The attempt at a solution
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## Distance Of Closest Approach

ok, will do
 Okay I have the same problem except my initial speed is 1.2*10^6 So, I used the equation 1/2mVo^2 = Kq^2/r I am solving for r and I keep getting 1.92 * 10^-13, but it is wrong. What am I doing wrong?
 Mentor Blog Entries: 1 Realize that both protons are moving and thus have kinetic energy.
 So, I am using the wrong formula? Not getting it...
 Mentor Blog Entries: 1 You need to set total KE equal to PE.
 I thought that is what I did
 Mentor Blog Entries: 1 What's the KE of each proton? (Symbolically--no need for numbers yet.)
 I am not sure what you are looking for

Mentor
Blog Entries: 1
 Quote by nckaytee I am not sure what you are looking for
The basic expression for the KE of each proton, like you used in post #5.
 1/2mVo^2

Mentor
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 Quote by nckaytee 1/2mVo^2
Good. That's the KE of one proton. So what's the total KE of both protons?
 so, 1/2mVo^2 + 1/2mVo^2= Kq^2/r ?
 Mentor Blog Entries: 1 Good.
 Okay I got the correct answer 9.6e-14 .... finally :-)