Question

The velocity of water in a river is $18\, km/hr$ near the surface. If the river is $5\, m$ deep, find the shearing stress between the horizontal layers of water. The co-efficient of viscosity of water $= 10^{-2}$ poise.

• A. $10^{-1} \,N/m^{2}$
• B. $10^{-2} \,N/m^{2}$
• C. $10^{-3} \,N/m^{2}$
• D. $10^{-4} \,N/m^{2}$

Answer 1

Answer: (C)

Velocity of a layer of water, $V =\frac{5}{18} 18=5\, m / s$
Also, $\eta=10^{-2}$ poise $=10^{-3} \frac{ Ns }{ m ^{2}}$
Shear stress, $\tau=\eta \frac{ V }{ d }=10^{-3} X 5 / 5=10^{-3} \frac{ N }{ m ^{2}}$