Consider the free vibration of the uniform slender bar with mass $m$. Use $m = 10$ kg, $k = 4$ kN/m, $c = 20$ J/m, $F_0 = 100$ N, and $\omega = 10$ rad/s.
1) Drive the equation of motion (EoM),
2) Propose a possible solution to EoM with the initial condition of no velocity and displacement at the beginning, and
3) Find the natural frequency ($\omega_n$) of the system.