two spherical objects are separated by a distance of 9x10^-3 m. The objects are initially electrically neutral and are very small compared to the distance between them. Each object acquires the same negative charge due to the addition of electrons. As a result, each object experiences an electrostatic force that has a magnitude of 4.55 x 10^-21 N. How many electrons did it take to produce the charge on one of the objects?

Question

the answer is 40 electrons but i have no idea how to do it

Answer 1

From the force, and coulomb's force equation, solve for q^2 then q.

divide q by e, the charge on one electron to get the number of electrons.