Ans: C
Let $V_0$ and $V_1$ be the volume of the cylinder of radius $R$ and that of the cylinder of radius $r$ respectively. Then we have $V_0=2V_1$. Since the heights of the two circular cylinders are the same, then we have
Let $V_0$ and $V_1$ be the volume of the cylinder of radius $R$ and that of the cylinder of radius $r$ respectively. Then we have $V_0=2V_1$. Since the heights of the two circular cylinders are the same, then we have
$\begin{array}{rcl}
\dfrac{V_0}{V_1} & = & \left( \dfrac{R}{r} \right)^2 \\
\dfrac{2V_1}{V_1} & = & \left( \dfrac{R}{r} \right)^2 \\
\dfrac{R}{r} & = & \sqrt{2} \\
R:r & = & \sqrt{2} : 1
\end{array}$