using WET $\begin{aligned}
& \mathrm{W}{\mathrm{g}}=\mathrm{k}{\mathrm{f}}-\mathrm{k}{\mathrm{i}} \
& \mathrm{Mg} \mathrm{~L} \sin \theta=\mathrm{k}{\mathrm{f}}-\mathrm{k}{\mathrm{i}}
\end{aligned}K.E.inpurerolling\frac{1}{2} \mathrm{mV}{\mathrm{cm}}^2+\frac{1}{2} \mathrm{I}{\mathrm{cm}} \omega^2\begin{aligned}
& =\frac{1}{2} \mathrm{mV}^2+\frac{1}{2} \times \frac{2}{5} \mathrm{mR}^2 \frac{\mathrm{~V}^2}{\mathrm{R}^2} \
& \frac{7}{10} \mathrm{mV}^2
\end{aligned}\mathrm{mgL} \sin \theta=\frac{7}{10} \mathrm{mV}{\mathrm{f}}^2-0\begin{aligned}
& \mathrm{V}_{\mathrm{f}}^2 \propto \sin \theta \
& \left(\frac{\mathrm{V}_1}{\mathrm{V}_2}\right)^2=\frac{\sin \theta_1}{\sin \theta_2}=\frac{\sin 30^{\circ}}{\sin 45^{\circ}}=\frac{1}{\sqrt{2}}
\end{aligned}$