The viscous drag acting on a metal sphere of diameter $1 \mathrm{~mm}$, falling through a fluid of viscosity…
The viscous drag acting on a metal sphere of diameter $1 \mathrm{~mm}$, falling through a fluid of viscosity $0.8 \mathrm{~Pa} s$ with a velocity of $2 \mathrm{~m} \mathrm{~s}^{-1}$ is equal to
$1.5 \times 10^{-3} \mathrm{~N}$
$20 \times 10^{-3} \mathrm{~N}$
$15 \times 10^{-3} \mathrm{~N}$
$30 \times 10^{-3} \mathrm{~N}$
Solution
Viscous drag acting on sphere is given by
$\begin{aligned} F_V & =6 \pi \eta r V \\ & =6 \times \frac{22}{7} \times 0.8 \times \frac{10^{-3}}{2} \times 2 \\ & =15.08 \times 10^{-3} \mathrm{~N} \\ & \simeq 15 \times 10^{-3} \mathrm{~N}\end{aligned}$
.