Question

The average velocity of the tube of area a is given by _________

(a) \(v_{av}=\frac{iγ_w}{8ηπ}a \)

(b) \(v_{av}=\frac{\frac{iγ_w}{8ηπ}}{a}\)

(c) \(v_{av}=\frac{iγ_w}{2ηπ}a\)

(d) \(v_{av}=\frac{\frac{iγ_w}{4ηπ}}{a}\)

I have been asked this question in a national level competition.

This question is from Poiseuille’s Law in portion Permeability of Geotechnical Engineering I

Answer 1

Correct choice is (a) \(v_{av}=\frac{iγ_w}{8ηπ}a \)

To explain I would say: The average velocity is given by,

Vav=q/a

Vav=q/πr^2

Substituting for q,

∴ \(v_{av}=\frac{iγ_w}{8ηπ}a. \)