I have this question that initially a metal ball of radius r1 with potential v1, then surrounded by a conducting shell with radius r2. Find potential of ball if shell grounded. So v1 =kq/r1, then q=vr1/k, can I say directly that shell will have -q since it's induced by ball? Then v ball will be kq /r1 + k(-q)/r2 ? I'm not sure if I find should count the potential due to shell when I find the v ball? Thanks for help.