Asmall glass ball rubbed with silk gains a charge of 2.0 uc. the glass ball is placed 12 cm from a small charged rubber ball that carries a charge of -3.5 uc. a. what is the magnitude of the electric force between the two balls?

The electric force between the two balls is given by:

where
is the Coulomb's constant
q1 and q2 are the charges of the two balls
r is the separation between the two balls

In our problem, we have 

(we can neglect the sign of the charge, since we are only interested in the magnitude of the force)

Therefore if we use the previous equation, we can find the electrostatic force between the two balls:

The answer is orbit around nucleus