d
\(\mathrm{K}=\frac{1}{2} \mathrm{mv}^{2} ; \mathrm{U}=\frac{1}{2} \mathrm{k} \mathrm{x}^{2}=\frac{1}{2} \mathrm{m}^{2} \mathrm{x}^{2}\)

\(\begin{aligned} \therefore \quad \frac{\mathrm{k}}{\mathrm{U}}= \frac{\mathrm{v}^{2}}{\omega^{2} \mathrm{x}^{2}}=\left(\frac{\cos (\mathrm{wt})}{\sin (\mathrm{wt})}\right)^{2} \\ =\cot ^{2}\left(\frac{\pi}{90} \times 210\right) \\= \cot ^{2}\left(2 \pi+\frac{\pi}{3}\right) \\=\left(\frac{1}{\sqrt{3}}\right)^{2}=\frac{1}{3} \end{aligned}\)