A $250-$V$,1200$ r$/$min dc motor has a rated armature current $($IA$)$ of $170$ A and a rated field current $($IF$)$ of $5$ A$.$ Its armature resistance and field resistance are RA $=0\mathrm{.}06$ and RF $=50.$ In this motor, the brush voltage drop is assumed to be $2$ V$.$ There are $3625$ W of core losses, mechanical losses and stray losses. Find: $1)$ The output power of this motor at the rated condition; $2)$ The motor's efficiency at the rated condition.