Note: Please be careful with your signs of the potential and electron charge!
4 . C —The original force between the spheres is
When the spheres are brought into contact, they share a charge until they have the same electric
potential:
In addition, we know that Q 1 and Q 2 must add up to be the total original charge of 2Q:
Q 1 + Q 2 = 2Q
Substituting, we get
Calculating the new electrostatic force, we get the following: