A homogeneous 100-lb disk with radius R = 1 ft is attached to two identical cylindrical st...

A homogeneous 100-lb disk with radius R = 1 ft is attached to two identical cylindrical steel bars of length L = 1 It. The relation between the moment M exerted on the disk by one of the bars and the angle of rotation, θ, of the disk is

where J is the polar moment of inertia of the cross section of the bar and G = 1.7 × 109 lb/ft2 is the shear modulus of the steel. Determine the required radius of the bars it the frequency of rotational vibrations of the disk is to be 10 Hz.