(11) The line $l:(2 m+1) x+(m+1) y-7 m-4=0$ is intersected by the circle $C:(x-1)^{2}+$ $(y-2)^{2}=25$ to form the shortest chord length of $\qquad$ .
11 The line $l$ passes through the point $D(3,1)$. The center of the circle is $C(1,2)$, the shortest chord is perpendicular to $C D$, and $|C D|^{2}=5$, from which we can deduce that the half-chord length of the circle is $2 \sqrt{5}$, so the chord length is $4 \sqrt{5}$.