A shaft running at 900 rev/min is supported by bearings 50 mm in diameter and 75 mm in length. The bearings operate in still air. The oil used has a viscosity of 0.013 kg/ms and the diametral clearance is 0.05 mm. The permissible load corresponding to the heat generation of 35.8 watts is ZN [f=0.326(Z) (2)+ (a) 250 N (c) 450 N +0.002 (b) 350 N (d) 550 N