Question

Two spherical objects are separated by a distance of 2.97 × 10-3 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 1.67 × 10-21 N. How many electrons did it take to produce the charge on one of the objects?

I keep getting 567.68. What am I doing wrong?

Answer 1

F = kq^2/r
so q = sqrt(Fr/k)
q = 2.34e-17
each electron has a charge 1.6e-19
so you have about 146 electrons

Answer 2

everything is correct except the distance r should be squared. the number of electrons is much smaller than 146