Question

Calculate the viscous force acting on a rain drop of diameter 1 mm, falling with a uniform velocity 2 m/s through air. The coefficient of viscosity of air is 1.8 \(\times\) 10^-5 Ns/m²

Answer 1

Correct answer = 3.394 ×10^-7 N or 3.393 ×10^-7 N

Explaination::

Given: d= 1 mm, v₀ = 2 m/s, η= 1.8 × 10^-5 Ns/m²

r =d/2 =0.5 mm = 5 ×10^-4 m,

Solution:

 

By Stoke’s law the viscous force on rain drop is

f= 6πηr v₀

= 6 ×3.142 x 1.8 × 10^-5 x 5 ×10^-4 × 2

= 3.394 ×10^-7 N