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

$\begin {array} {1 1} (a)\;1 \times 10^{-2} & \quad (b)\;0.5 \times 10^{-2} \\ (c)\;1 \times 10^{-3} & \quad (d)\;0.5 \times 10^{-3} \end {array}$