physics
posted by John .
Im trying to study for my physics exam by doing some extra problems, however im stuck with this one. any help is much appreciated
Two tiny spheres have the same mass and carry charges of the same magnitude. The mass of each sphere is 4.62 x 106 kg. The gravitational force that each sphere exerts on the other is balanced by the electric force. Determine the charge magnitude.

Well, from experience, the charge has to be small.
gravitational force: GM^2/r^2
electrical force: kQ^2/r^2
set them equal.
Q^2=GM^2/k = you do it, then take the square root to find Q