
7.14. A point mass is suspended from a massless rigid bar as shown in Figure 7.26. The point mass is
subjected to white noise random forcing having a constant spectral density 0.008 N
2
m.
(a) How many degrees of freedom does this system have?
(b) Determine the root mean square of the responses. Use parameter values m = 3 kg, k
1
= 250
N/m, k
2
= 300 N/m, I
o
= 4 kg-m
2
, and L = 6 m.
Figure 7.26: A rigid bar and a point mass.
Solution: (a) This system has two degrees-of-freedom. It requires at least two independent coordinates to
completely define the motion of the system. There are many choices for the two coordinates, but here, we
will use the angle of rotation ...