Dynamics (matrix form)
With \(\mathbf{q}=\begin{bmatrix} x_1 & x_2 \end{bmatrix}^{\!T}\), \(\mathbf{M}\ddot{\mathbf{q}}+\mathbf{K}\mathbf{q}=\mathbf{0}\):
\[ \begin{bmatrix} m_1+\dfrac{J_1}{r^2} & 0 \\[6pt] 0 & m_2 \end{bmatrix} \begin{bmatrix} \ddot{x}_1 \\[4pt] \ddot{x}_2 \end{bmatrix} \;+\; \begin{bmatrix} 4k_1+k_2 & -k_2 \\[4pt] -k_2 & k_2 \end{bmatrix} \begin{bmatrix} x_1 \\[4pt] x_2 \end{bmatrix} \;=\; \begin{bmatrix} 0 \\[4pt] 0 \end{bmatrix} \]Energy
\[ T = \tfrac12\left(m_1+\frac{J_1}{r^2}\right)\dot{x}_1^2 + \tfrac12 m_2\,\dot{x}_2^2 \] \[ U = \tfrac12 k_1 (2x_1)^2 + \tfrac12 k_2 (x_2-x_1)^2 \]