A steel disk 300mm diameter of mass 29 kg is suspended from the end of a wire 2.5mm and 1.5m long , which is clamped into a central hole in the disk. The upper end of the wire been rigidly fixed or support when the disk is set in torsional vibration it is found to move oscillation in 78.2s. Fnd the modulus of rigidity of the wire and also calculate the amplitude of the oscillation which may be allowed if the maximum permissible density of the shear stress in the wire is 40MN/m