Question

two identical metal spheres carrying charge of + q and minus 2 q respectively now the spheres are allowed to touch and move back to the same situation find the new force of repulsion between them

Answer 1

Let the distance between the charges be r

Here q1 = q and q2 = -2q..

Note : when a sphere having charge q1 is being toched with another sphere of charge q2 and remove the spheres keeping them at the same location then charges gets distributed equally between them...

Net charge of each sphere
= ( q1 + q2 ) / 2
= {q + (-2q)} /2
= -q / 2
So Now charge on each sphere will be -q/2
here Distance between these charge is r..
see snap for more...

Hope this help.....