A massless bar of length $1 \mathrm{~m}$ is pivoted at one end and subjected to a force $F$ at the other end. Two translational dampers, with damping constants $c_{1}=10 \mathrm{~N}-\mathrm{s} / \mathrm{m}$ and $c_{2}=15 \mathrm{~N}-\mathrm{s} / \mathrm{m}$ are connected to the bar as shown in Fig. 1.109. Determine the equivalent damping constant, $c_{\mathrm{eq}}$, of the system so that the force $F$ at point $A$ can be expressed as $F=c_{\mathrm{eq}} v,$ where $v$ is the linear velocity of point $A$