 #1
feynman_fan
 7
 4
 Homework Statement

Two identical charges q are placed on the x axis, one at the origin and the other at x = 5.0 cm.
A third charge q is placed on the x axis so the potential energy of the threecharge system is the same as the potential energy at infinite separation.
What is the coordinate of the third charge?
 Relevant Equations
 ##U=q_0\cdot V=k\frac{q\cdot q_0}{r}##
I set up an equation for the sum of all the potential energies and when cancelling out ##k## and ##q^2##, I got ##\frac{1}{0.05}\frac{1}{x}\frac{1}{0.05x}=0##. However, this has no solutions, so I must've gone wrong somewhere. Could someone just give me a hint, not a solution, that would put me on the right track, because I want to really understand all the problems I do.