Question

The velocity of water in a river is $18km/hr$ near the surface. If the river is $5m$ 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

The correct option is C ${10}^{-3}N/m^2$

Velocity of a layer of water, $V=\frac{5}{18}18=5m/s$

Also,

$\eta ={10}^{-2}poise={10}^{-3}\frac{Ns}{m^2}$

Shear stress, $\tau =\eta \frac{V}{d}={10}^{-3}X5/5={10}^{-3}\frac{N}{m^2}$