$\begin{align}  & V=385{{m}^{3}} \\ & h=10m \\ & V=\pi {{r}^{2}}h \\ & 385{{m}^{3}}=\tfrac{22}{7}\times {{r}^{2}}\times 10 \\ & {{r}^{2}}=\frac{385{{m}^{3}}\times 7}{22\times 10m}=\frac{49}{4}c{{m}^{2}} \\ & r=\sqrt{\frac{49}{4}{{m}^{2}}}=\frac{7}{2}m \\ & diameter=2\times radius=2\times \frac{7}{2}m=7m \\\end{align}$