Calculating Forces on Two Charges Above a Conducting Sheet

[bon]

Homework Statement

Two charges +Q and -Q are a horizontal distance a apart and a vertical distance b above a large conducting sheet. Find the components of the forces acting on each charge.

Homework Equations

The Attempt at a Solution

Ok well I've tried to solve this using image charges (i.e. positing 2 imaginary charges below the plate) and have got an expression for F. My problem is that the expression is really horrible so i can't find the modulus of the vector bit and thus write it in components.. have i gone wrong?

my answer is F = kQ^2 times vector ( [1/a^2 - a/(a^2 + 4b^2)^3/2] , 0 , [2b/(a^2 + 4b^2)^3/2 - 1/4b^2] )

Thanks!

 

[gneill]

Those look like vector components from where I'm sitting!