An iron sphere of mass $20 \times 10^{-3}\;kg$ falls through a viscous liquid with terminal velocity $0.5\;ms^{-1}.$ The terminal velocity $(in\; ms^{-1})$ of another iron sphere of mass $54 \times 10^{-2}\;kg$ is :

Question

\[\begin {array} {1 1} (a)\;4.5 & \quad (b)\;3.5 \\ (c)\;2.5 & \quad (d)\;1.5 \end {array}\]