c
\(\frac{\mathrm{mv}^{2}}{\mathrm{r}}=\mathrm{mg} \sin \phi\)            \(...(i)\)

\(\mathrm{mg} \mathrm{r} \cos \theta=\frac{1}{2} \mathrm{mv}^{2}+\mathrm{rg} \sin \phi\)

\(\frac{\mathrm{v}^{2}}{\mathrm{rg}}=2 \cos \theta-2 \sin \phi \ldots \ldots(\mathrm{ii})\)

\(\sin \phi=2 \cos \theta-2 \sin \phi\)

\(3 \sin \phi=2 \cos \theta\)

\(\sin \phi=\frac{2}{3} \cos \phi\)