In a solid sphere , a point is located inside . While calculating potential at that inernal point , we follow two steps . We have a sphere above which the point lies and a part of sphere below which the point lies . We calculate potential separately for both cases and add them up .
But my confusion lies in the procedure of the ways .In first case , we simply express mass by density and put in the potential formula . But in the second case , we follow calculus . We divide the sphere into infinitesimal rings and integrate them .
But my question is , why are separate methods followed ?