Electric Potential/Work - POint Charges on a Square

[alicemunro]

Homework Statement

two identical point charges are on diagonally opposite corners of a square that is 0.5m on a side. Each charge is +3 x 10^ -6 C. How much work is done by the electric force when 1 charge moves to an empty corner?

Homework Equations

W= u= qV = q(kq/r) = kq^2/ r (is this right??)

The Attempt at a Solution

w= kq^2 / r = (k)(+3 x 10^ -6)^2 / (.5)

the real answer is -4.7 x 10^-2 but i don't know how to get that. thanks

 

[Delphi51]

Almost! It is the "W = u" part where you err. This U is the potential energy. The work done is the difference between the U at the beginning point and the U at the ending point.
You already have it half done.