$$XPQY$$ is a vertical smooth long loop having a total resistance $$R$$ where $$PX$$ is parallel to $$QY$$ and separation between them is $$l$$. A constant magnetic field $$B$$ perpendicular to the plane of the loop exists in the entire space. A rod $$CD$$ of length $$L (L > l)$$ and mass $$m$$ is made to slide down from rest under the gravity as shown in figure. The terminal speed acquired by the rod is _______ $$m/s. (g$$ = acceleration due to gravity)