I need some help:

In the figure below, the two ends of a U-shaped wire of mass m = 13.0 g and length L = 13.0 cm are immersed in mercury (which is a conductor). The wire is in a uniform field of magnitude B = 0.0900 T. A switch (unshown) is rapidly closed and then reopened, sending a pulse of current through the wire, which causes the wire to jump upward. If jump height h = 3.50 m, how much charge was in the pulse? Assume that the duration of the pulse is much less than the time of flight.