The viscous drag acting on a metal sphere of diameter 1 mm, falling through a fluid of viscosity 0.8 Pa  with a velocity of 2 ms^-1 is equal to :

According to Stoke’s law, viscous force acting on a spherical body moving with a velocity ‘v’ in a liquid of coefficient of viscosity. $\eta$ is
$F_v=6\pi \eta rv$
Where r is the radius of the sphere.
${\mathrm{F}}_{\mathrm{v}}=6\pi \eta \mathrm{rv}=6\pi \left(0.8\right)\left({10}^{-3}\right)2=9.6\pi \times {10}^{-3}=30\times {10}^{-3}\mathrm{N}\text{.}$