Consider the torsion-bar suspension shown in Figure 4.1.6. Assume that the torsion bar is a steel rod with a length of 4 ft and diameter 1.5 in. The wheel weighs 40 lb and the suspension arm is 2 ft long. Neglect the masses of the torsion bar and the suspension arm, and calculate the natural frequency of the system. Use G = 1.7 x 109 lb/ft2.