A thin spherical pressure vessel of 200mm diameter and 1mm thickness is subjected to an internal pressure varyding from 4 to 8MPa. Assume that the yield, ultimate and endurance strength of material are 600, 800, 400MPa respectively. The factor of safety as per Godman’s relation is
(a) 2.0 (b) 1.6 (c) 1.4 (d) 1.2