A metallic ring of mass m and radius l (ring being horizontal) is
falling under gravity in a region having a magnetic field. If z is the
vertical direction, the z-component of magnetic field is B_z = B_o
(1+λ z). If R is the resistance of the ring and if the ring falls with a
velocity v, find the energy lost in the resistance. If the ring has
reached a constant velocity, use the conservation of energy to
determine v in terms of m, B, λ and acceleration due to gravity g.