$27\mathrm{.}56$ CP A $2\mathrm{.}60$ N metal bar, $0\mathrm{.}850$ m long and having a resistance of $10\mathrm{.}0,$ rests horizontally on conducting wires connecting it to the circuit shown in Fig. P$27\mathrm{.}565.$ The bar is in a uniform, horizontal, $1\mathrm{.}60$ T magnetic field and is not attached to the wires in the circuit. What is the acceleration of the bar just after the switch $S$ is closed?

Figure P$27\mathrm{.}56$