$\begin{align}  & v=\sqrt{\frac{F}{\mu }}\xrightarrow[m=\rho V=\rho AL]{\mu =\frac{m}{L}}v=\sqrt{\frac{F}{\rho A}}\xrightarrow{A=\pi {{R}^{2}}} \\  & v=\frac{1}{R}\sqrt{\frac{F}{\rho \pi }} \\  & \xrightarrow[{{R}_{A}}=\frac{1}{2}{{R}_{B}}]{\rho A=2\rho B,{{F}_{A}}={{F}_{B}}}\frac{{{v}_{A}}}{{{v}_{B}}}=\frac{{{R}_{B}}}{{{R}_{A}}}\sqrt{\frac{\rho B}{\rho A}}=2\sqrt{\frac{1}{2}}=\sqrt{2} \\ \end{align}$