Chapter 10.2, Problem 10.73P

Using the method of Sec. 10.2C, solve Prob. 10.39. Determine whether the equilibrium is stable, unstable, or neutral. (Hint: The potential energy corresponding to the couple exerted by a torsion spring is $\frac{1}{2}K{\theta }^2$, where K is the torsional spring constant and θ is the angle of twist.)

10.39 The lever AB is attached to the horizontal shaft BC that passes through a bearing and is welded to a fixed support at C. The torsional spring constant of the shaft BC is K; that is, a couple of magnitude K is required to rotate end B through 1 rad. Knowing that the shaft is untwisted when AB is horizontal, determine the value of θ corresponding to the position of equilibrium when P = 100 N, l = 250 mm, and K = 12.5 N·m/rad.

Fig. P10.39