Exercise 6.4 [ 0.857[Hz] ] In the linkage shown below, the bars AB and CD are uniform in section and each has a mass of 1.2 [kg], while the disc at D, carried by the bar CD, is 150 [mm] in diameter and has a mass of 1 [kg]. The mass of link BE is 1 [kg], the spring has a mass of 1.5 [kg] and a stiffness of 400[N//m]. Find the natural frequency of vibration of the system for small oscillations. Please solve it,the answer is supposed to be 0.857Hz