Very very urgent please help me...
A small ball with mass =0,4g charged with electricity= 3x10^(-10) coulomb is united with the edge of a silk rope with length=8cm. The other edge of the rope is on a big insulating material with concentration of the electric energy: 25x10^(-6) c/m^2 . Find the angle between the rope and the big insulating material, if the ball is at a balanced condition.