A flat disk of outer radius b-125mm and inner radius a=25mm is shrink-fitted onto a shaft of radius 25.05mm. Both members are made of steel with E=200Gpa, v=0.3, and p=7.8 KN.s2/m4. Determine (a) the speed in rpm at which the interface pressure becomes zero and (b) the radial wall thickness and (b) the maximum stress at this speed.