m D 11. Consider a 1 DOF system with a rigid block of mass m that can move only in the horizontal direction, as shown in the above figure. The system is at the static equilibrium: THE FINITE ELEMENT METHOD: A PRACTICAL COURSE a. Give the expressions for the strain potential energy, work done by external forces, and the total potential energy. b. Derive the equilibrium equations for the system using the minimum potential energy principle. c. Show that the total potential energy of the 1DOF system is at a minimum at the equilibrium position.