A horizontal, 30-cm-long conducting rod is rolling along two conducting rails that are parallel to the x-axis. The rod is parallel to the y-axis, but moves in the +x direction with a speed of 3.3 m/s . The rails are electrically connected by a second conducting rod attached to the rails at an x-coordinate smaller than that of the rod.

The entire assembly is immersed in a uniform magnetic field of 0.4 T in the +z direction (up). An emf is developed by the moving conductor. The moving rod has a resistance of 2.1 ohms, while the resistance of the circuit-closing rod and rails in series with the rod is 89 ohms. The emf drives a current around the circuit. Neglecting friction, what force (in Newtons) is needed to keep the rod moving at a constant speed?