a metal bar of mass m slides frictionlessly on two parallel conducting rails a distance l apart as shown in the figure. a resistor r is connected across the rails, and a uniform magnetic field b, pointing into the page, fills the entire region. (a) if the bar moves to the right at speed v, what is the current in the resistor? in what direction does it flow? (b) what is the magnetic force on the bar? in what direction? (c) if the bar starts out with speed vo a time 0, and is left to slide, what is its speed a later time t? (d) the initial kinetic energy of the bar was, of course, ½mvg . check that the energy 0 and the time when the bar stops is exactly delivered to the resistor between mv