In Milikan's oil drop experiment,what is the terminal speed of an uncharged drop of radius $2\times 10^{-5}m$ and density $1.2\times 10^3Kgm^{-3}$?Take the viscocity of air at the temperature of the experiment is $1.8\times 10^{-5}pas$.How much is the viscous force on the drop at the speed?Neglect byoyancy of the drop due to air.

Question

$\begin{array}{1 1}(A)\;4cm/s,4.2\times 10^{-10}N\\(B)\;4.8cm/s,8\times 10^{-9}N\\(C)\;5.8cm/s,3.9\times 10^{-10}N\\(D)\;5cm/s,3.8\times 10^{-9}N\end{array}$