4) Determine the critical speed of rotation for the overhanging 2-in. diameter steel shaft (E=29 X 106 psi) with attached 60-lb grinding wheel shown in Figure 3. Pillow block bearing 20 in. 12 in. Steel shaft Grinding wheel, 60 lb 5) Determine the new shaft diameter required, if the critical speed calculated in Problem 4) is unacceptable and the minimum critical frequency must be at least 75Hz.