Calculating Charges Using Coulomb's Law and Slope Analysis

[dba]

Homework Statement

In our physics lab about the Coulomb's law we had an Van de Graaff Generator (VdGG) to produce a charge and we had a sphere covered with foil (a conductor) which was hang up next to the VdGG. When the VdGG produced charged the sphere was attracted to it and finally touched th VdGG and became charged also. The result was that the sphere then was repelled.
We took measurements of the process and then drew a graph, from which we received a slope (of a straight line)
We did 5 trails, and receive data for 1/r^2 and F for each trail.

Homework Equations

The question is: From the slope, using Coulomb's law with the given force constant k = 9x10^9 nm^2/C^2, determine the charge Q on the speres in the units Coulomb.

The Attempt at a Solution

So, the Coulomb's Law is:

F = k * |Q1|*|Q2|\r^2

The slope = k * |Q1|*|Q2| = 3.81x10^-4 Nm^2

So the charges Q are
|Q1|*|Q2| = slope/k

I do not know how I can calculate the single charges.

Thanks for any help!

 

[Antiphon]

When the balls touch, they attain the same voltage. Each is a different capacitor. You can use
Q1*C1 = Q2*C2 = V.

There may be an easier way, let's hear from others too since you don't seem to have lab data on both electrodes.