$2)$ An electron moving perpendicular to a uniform magnetic field of $3\mathrm{.}210-2$ T moves in a circle of

radius $0\mathrm{.}40$ cm$.$ How fast is this electron moving? $($mel $=9\mathrm{.}1110-31$ kg$,$ e $=1\mathrm{.}6010-19$ C$)$

A$)2\mathrm{.}2107$ m$/$s

B$)1\mathrm{.}910-2$ m$/$s

C$)1\mathrm{.}910-30$ m$/$s

D$)3\mathrm{.}0106$ m$/$s