A moving rod has a resistance of 0.25 ohms and moves on rails 20.0 cm apart. The stationary U-shaped conductor has negligible resistance. When a force of 0.350 N is applied to the rod, it moves to the right at a constant speed of 1.50 m/s. What is the magnetic field? (I know how to find this part out but need help with the second part of the question which is below)

Also, take B and everything else from the previous question and find out how fast the bar is dropping if v is constant. The mass of the bar is 125 g. And the space between the rails is 20.0 cm.