Question

Rain drop of radius $0.2mm$ falling with velocity of $2m/s$. If coefficient of viscosity of air is $1.8\times {10}^{-4}Ns/m^2$, determine viscous force acting on the drop.

Answer 1

Viscous force $F=6\pi \eta rv$

So, $F=6\pi \times 1.8\times {10}^{-4}\times 0.2\times {10}^{-3}\times 2$

$⟹F=1.36\times {10}^{-6}N$