2. Consider a 2 DOF system with two rigid blocks that can move only in the horizontal direction, as shown in the following figure. (1) Give the expressions for the strain (potential) energy (7), work done by external forces (W), and the total potential energy (I-II-W). (2) Drive the equilibrium equations for the system using the minimum potential energy principle. m1 fi ►D₁ m2 Fr D2