F = weight = m g = k q^2/d^2
so
d = sqrt [ k q^2 /(m g) ]
where d is distance between balls (actually between centers of balls if charges were uniformly charged around but they will not be because like charges repel and the charges would be pushed to the far side of each ball but we do not know what the radius is so ignore all that. Moreover no way the ball would remain there, that is unstable equilibrium and the slightest breath of wind or whatever would wreck the whole experiment. Oh well, whatever)
Two Ping-Pong balls each have a mass of 2.6g and carry a net charge of 0.500ìC . One ball is held fixed.
At what height should the second ball be placed directly above the fixed ball if it is to remain at rest there?
Express your answer to two significant figures and include the appropriate units.
Thanks, James
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