What Speed Must an Electron Achieve to Orbit a Charged Sphere?

[dtesselstrom]

Homework Statement

A 2.40 -mm-diameter glass sphere has a charge of + 1.70 nC.
What speed does an electron need to orbit the sphere 1.40 mm above the surface?

Homework Equations

Electric Field of Sphere: E=k*Q/(r^2)
q*E=M*v^2/r

The Attempt at a Solution

It seems pretty straight forward but I must be doing something wrong with the r values. Could someone tell me what the radius is considered. For the electric field is it the radius of sphere + the distance away or what and same for the other equation. I've tried pretty much all the combos I can think of and still am getting it wrong so not sure where I am going wrong.

 

[Mindscrape]

It says above the surface so you would have to add the radius of the sphere to the radius of the orbit.