Question

Water in a river $20m$ deep is flowing at a speed of $10m{s}^{-1}$. The shearing stress between the horizontal layers of water in the river in $N{m}^{-2}$ is :(coefficient of viscosity of water $={10}^{-3}$ SI units)

• A. $1\times {10}^{-2}$
• B. $0.5\times {10}^{-2}$
• C. $1\times {10}^{-3}$
• D. $0.5\times {10}^{-3}$
  

Answer 1

The correct option is D $0.5\times {10}^{-3}$

$\frac{F}{A}=$ shearing stress $=\eta \frac{dv}{dx}$
$\frac{dv}{dx}=\frac{10m{s}^{-1}}{20}=0.5$
$\therefore$ shearing stress $=0.5\times {10}^{-3}$