Consider the possibility of a new design for an electric train.  The train is driven by a force 
of the vertical component of the Earth's magnetic field (~50uT) on a conducting axle 3.0 m long.
The current passes through one rail, up a conducting wheel, through the axle, down the other wheel,
and through the other rail back to the power supply at the end of the rail line.  
<ol type=a>
<li> What current is needed to provide a 10 kN force?
<li> How much power is lost (to heating) for each Ohm of resistance in the rails and the axle?
<li> Is such a design realistic?
</ol>