$1\mathrm{.}5$ m$/$s with its $85-$cm$-$wide head perpendicular to the earth$$s $50$ mT magnetic field. What is the magnitude of the emf induced between the two sides of the shark$$s head?

$3.||$ A $10-$cm$-$long wire is pulled along a U$-$shaped conducting rail in a perpendicular magnetic field. The total resistance of the wire and rail is $0\mathrm{.}20.$ Pulling the wire with a force of $1\mathrm{.}0$ N causes $4\mathrm{.}0$ W of power to be dissipated in the circuit.

a$.$ What is the speed of the wire when pulled with a force of $1\mathrm{.}0$ N$?$ b$.$ What is the strength of the magnetic field?