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Velocity of water in a river is...

Velocity of water in a river is

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As velocity at the bottom of the river will be zero, velocity gradient,
`( dv)/( dy ) = ( 18 xx 10^(3))/( 60 xx 60 xx 15 ) = 1 s^(-1)`
Now as the viscous force `F = eta A ( dv //dy)` is tangential to the area, Shear stress `= ( F_(11))/( A) = eta( dv)/( dy)`
`= 10^(-3) xx 1 = 1 xx 10^(-3) N//m^(2)`
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