$2.$ The system shown in the following figure includes a mass, a rigid and massless bar, and a spring. The bar can rotate freely around a hinge. We assume that the rotational angle $\backslash (\backslash$theta $\backslash )$ is small. At the position $\backslash (\backslash$theta$=0\backslash )$ the spring is unstretched. Find the equation of motion by using conservation of mechanical energy $($linearize your equation$)(25$ points$).$