$3\mathrm{.}2\mathrm{.}20$ Water flows down the face of the dam shown in Fig. P$3\mathrm{.}2\mathrm{.}20.$ The face of the dam consists of two circular arcs with radii of $3$ and $6$ m as shown. If the speed of the water along streamline $A-B$ is approximately $V=(2gh{)}^{\frac{1}{2}},$ where the distance $h$ is as indicated, plot the normal acceleration as a function of distance along the streamline, $a_n=a_n(s).$