A $0\mathrm{.}50-$kg object moves in a horizontal circular track with a radius of $2\mathrm{.}5$ m$.$ An external force of $3\mathrm{.}0$ N$,$ always tangent to the track, causes the object to speed up as it goes around. If it starts from rest its speed at the end of one revolution is:O $5\mathrm{.}5$ m$/$sO $14$ m$/$s $15$ m$/$sO $18$ m$/$s $21$ m$/$s