The shape of an elastic rod of length \( l \) is represented by the position vector \( \vec{r}(s) \) corresponding to the arc length \( s \). If the bending energy of the rod is
\[
E = K \int_0^l \left( \frac{\partial^2 \vec{r}}{\partial s^2} \right)^2 \, ds,
\]
what is the dimension of \( K \) in terms of mass \( M \), length \( L \), and time \( T \)?