# Homework Help: Electric Potential

1. Jun 1, 2009

### bob19841984

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

A point charge of +8C is located at (-6,0)cm. A second point charge of -11C is located
at(-5,-12)cm. If a -5C charge were at the origin, how much energy is required to move it to in nity?

2. Relevant equations

V=KQ/R
U = -qV

3. The attempt at a solution
I have the solution. It is given as below... I just dont understand why!
http://a-s.clayton.edu/jdyer/physics/phys1112/phys1112S09/Quizzes/1112_Quiz2_solution.pdf" [Broken]

If the origin now has a -5 micro C charge, why is the energy potential still calculated as if it was not there? I have been banging my head on this for a while, any help would be greatly appreciated.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

Last edited by a moderator: May 4, 2017
2. Jun 1, 2009

### rl.bhat

V1 and V2 are the potentials at origin due to two charges. -5 μC charge is taken from origin to infinity and the work done to do this is -q*ΔV.

Last edited by a moderator: May 4, 2017