Consider a situation in which there is a Newtonian fluid between two long coaxial uniformly moving cylinders of radius $R$ and $2R$.

 

A steel ball is dropped in a viscous liquid. The distance of the steel ball from the top of the liquid is shown below. The terminal velocity of the ball is closest to

A raindrop with radius $\mathrm{R}=0.2 \mathrm{mm}$ falls from a cloud at a height $\mathrm{h}=2000 \mathrm{m}$ above the ground. Assume that the drop is spherical throughout its fall and the force of buoyance may be neglected, then the terminal speed attained by the raindrop is : [Density of water $f_{\mathrm{w}}=1000 \mathrm{kg}{ \mathrm{m}}^{-3}$ and Density of air $f_{\mathrm{a}}=1.2 \mathrm{kg}{ \mathrm{m}}^{-3}, \mathrm{g}=10 \mathrm{m}/{\mathrm{s}}^2$ Coefficient of viscosity of air $\left.=1.8\times {10}^{-5}\mathrm{N} \mathrm{s} {\mathrm{m}}^{-2}\right]$