For true centrifugal casting process with the axis of rotation in horizontal direction, an acceleration of 75g, where g is the acceleration due to gravity, is required for sound casting the relation between diameter ‘D’ (in mm) and the rotational speed N(1rev/s) for this casting is N2D = constant, determine the constant. Also calculate the mold speed (in rev/se© for casting CI pipes of 5m long with outside and inside diameters of 0.52m and 0.5m respectively.