Two spherical objects with a mass of 2.88 kg each are placed at a distance of 2.12 m apart. How many electrons need to leave each object so that the net force between them becomes zero?

Answer 1

G•m²/R =k•q²/R,
q=m•sqrt(G/k)=
=2.88•sqrt(6.67•10^-11 /9•10^9) =2.48•10^-10 C,
N =q/e=2.48•10^-10/1.6•10^-19 =1.55•10^9