[Experts only: 4th repost] The force between copper ball and point charge?

Question

What is the force of electric interaction between a copper ball
of radius R carrying net charge +Q, and a point charge +3Q
located at distance 2R from the center of the ball?

"The charge will be evenly distributed in a conductor, so the overall effect will be the same as a point chage at the center"

This statement is valid only in absence of
other external electric fields. The point charge +3Q in the vicinity violates equpotentiality on surface of the copper ball. Net charge +Q of the ball will have to redistribute and restore equipotentiality.

Answer 1

Use the equation
F = k Q1 Q2 / r^2
The direction of the force is along the axis between the centers of the two charges.
k = 1 / (4 pi eo), where eo is permittivity. In air, it's 8.854E-12 F/m
Q1 is the charge on the first object, Q2 is the charge on the second. (charge is in coulombs)
r is the distance between the charges.

Use the distance between the center of the copper ball, and the point charge. The charge will be evenly distributed in a conductor, so the overall effect will be the same as a point chage at the center.