Electrostatic Potential of 4 charged spheres on corners of a square

[sweetdion]

Homework Statement

Four idential charged spheres are located at the corners of a square with side length 2a. The spheres are much smaller than the size of the square (r<<a) and each sphere has a mass m and carries the same charge -Q.

a) What is the total electrostatic potential energy of the combined 4-sphere system when arranged as described?
b) How much kinetic energy does a sphere gain by moving very far away from the other three?
c) What is the speed of a sphere moved very far away?

Homework Equations

Utot=kq1q2/r
KEf=Ui
KE=1/2mv^2

The Attempt at a Solution

For part a, I think i got the right answer: Utot=k(4root2q^2+2q^2)/root2r

b)KE=1/2(4m)v^2 and that's it because that's all we know

c) I used Ui=Kf
so k(4root2q^2+2q^2)/root2r=1/2(4m)v^2

and solve for v to get

v=squareroot(k*2q^2/mr+q^2/root2mr)

 

[sweetdion]

im just wanting to know if I am right