Calculating Work for a Dipole: 90J

[HenryHH]

Homework Statement

A dipole with ±6.0 μC charges is positioned so that the positive charge is 1.0 mm to the right of the origin and the negative charge is at the origin. How much work does it take to bring a 10.0 μC charge from infinity to a position x = 3.0 mm, y = 0.0 mm? (The value of k is 9.0 × 10^9 N∙m2/C2.)

Homework Equations

The potential of an electric dipole: V = kq(1/r+ - 1/r-)

The Attempt at a Solution

I think I know how to do this problem, but I have some questions. Are r+ and r- the distances the 10 uC charge is from the positive and negative dipole charges, respectively? The answer to the problem is 90J, but I keep getting something like .0000000009, so I'm wondering what I'm doing wrong here.

 

[gneill]

Usually when one's result is off by some multiple of 10 it's due to a problem with unit conversions. Can you show your math?