\(\mathrm{U}_{\mathrm{i}}+\mathrm{K}_{\mathrm{i}}=\mathrm{U}_{\mathrm{f}}+\mathrm{K}_{\mathrm{r}}\)
\(\Rightarrow \mathrm{mg} \frac{\ell}{2} \sin 30^{\circ}+0=0+\frac{1}{2} \mathrm{I} \omega^{2}\)
\(\Rightarrow \operatorname{mg} \times \frac{1}{2} \times \frac{1}{2}+0=0+\frac{1}{2} \times \frac{\mathrm{m}(1)^{2}}{3} \omega^{2}\)
\(\Rightarrow \omega^{2}=\frac{3 \mathrm{g}}{2} \Rightarrow \omega=\sqrt{15}\)
\(\therefore n=15\)