At what distance of separation must two 1.00-microCoulomb charges be positioned in order for the repulsive force between them to be equivalent to the weight (on Earth) of a 1.00-kg mass?
##303mm##
From of Electrostatic forces between charged objects we get that
##F=k(Q_1Q_2)/r^2##
##therefore r = sqrt((kQ_1Q_2)/F)##
##=sqrt((9xx10^9)(1xx10^(-6))^2)/(98)##
##=303mm##
(Note that the weight force is given by ##W=mg=1xx98=98N##)