Electric Force/ charge problem; missing electrons

[UltrusViderat]

Homework Statement

How many electrons are missing from a pith ball which feels an electrostatic force of
4.5 x 10^-3 N torward a second pith ball 22 mm away with a net charge of 2.3 nC.

Homework Equations

q= ne; charge of an object equals the number of electrons x the charge of an electron

F= kqq/r^2

The Attempt at a Solution

F= kqq/r^2
q=(Fr^2)/kq

q=((4.5 x 10^-3 N)(0.022 m)^2)/((8.99 x 10^9)(2.3 x 10^-9))

q=1.05 × 10^-7
q=ne

(1.05 x 10^-7)/(1.6 x 10^-19)= 658,000,000,000= 6.58 x 10^11 electrons ? Is that right?

 

[SammyS]

It looks good except it should be a repulsive force, if electrons are missing.

Plugging the unknown charge back in gives the Force OK.