3. an 8-inch diameter steel shaft is force fit into a cast iron disk with a 20-inch outside diameter. the maximum tangential stress in the disk is 5000 psi. if esteel = 30x106 psi and ecast iron = 15x106 psi, with poisson’s ratio  for both materials equals to 0.3, (a) determine the contact pressure required between the shaft and the disk (a: p  3621 psi ). (b) determine the decrease in the radius of the shaft (a: ds = 0.00034 inch). (c) determine the required diametral interference (a: 2 = 004 in. (hint: a change in the shaft radius or diameter can be obtained through the displacement in the shaft)