17. A shaft ABC of 700 mm length and 50 mm external diameter is bored, for a part of its length AB, to a 30 mm diameter and for the remaining length BC to 40 mm diameter bore. If the shear stress is not to exceed 80 N/mm?, find the maximum power, the shaft can transmit at a speed of 200 r.p.m. If the angle of twist in the length of 20 mm diameter bore is equal to that in the 30 mm diameter bore, find the length of the shaft that has been bored to 20 mm and 30 mm diameter. 18. A hollow Wrought Iron column of outside diameter is 400 mm has a thickness of 50 mm. it is 9 m long and is fixed at both ends. Calculate the safe load by Rankine's formula using a factor of safety of 4. Calculate the slenderness ratio and the ratio of Euler's and Rankine's critical loads. Take oc = 250 N/mm2 and a =1/9000 in Rankine's formula and E = 210 GPa. 19. Two shafts are connected end to end by means of a flanged coupling in which there are 12 bolts, the pitch circle diameter being 30 cm. the maximum shear stress is limited to 55 N/mm in the shafts and 20 N/mm2 in the bolts. If one shaft is solid of 7 cm diameter and the other is hollow of 12 cm external diameter, calculate the internal diameter of the hollow shaft and the bolt diameter so that both shafts and the coupling are all equally strong in torsion.