7.7   A metal bar of mass m slides frictionlessly on two parallel conducting rails a distance l apart (Fig 7.16). A resistor R is connected across the rails and a uniform magnetic field B, pointing into the page, fills the entire region.

Figure 7.16

1. If the bar moves to the right at a speed v, what is the current in the resistor? In what direction does it flow?

2. What is the magnetic force on the bar? In what direction?

3. If the bar starts out with a speed v_o at time t = 0, and is left to slide, what is its speed at a later time t?

4. The initial kenitic energy of the bar was, of course, 0.5 mv_o². Check to see that the energy delivered to the resistor is exactly 0.5 mv_o².