In Figure, a conducting rod of mass m and negligible resistance is free to slide without friction along two parallel rails of negligible resistance separated by a distance l and connected by a resistance R. The rails are attached to a long inclined plane that makes an angle ? with the horizontal. There is a magnetic field B directed upward.

(a) Show that there is a retarding force directed up the incline given by F = (B2?2 v cos2 ? )/R.

(b) Show that the terminal speed of the rod is v = (mgR sin ?)/( B2?2cos2 ?).