The velocity of water in a river is 18 km near the surface. If the river is 5m deep find the shearing stress between the horizontal layer of water in
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the minus sign is indication of frictional force which is opposite to the direction of motion
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The shearing stress between the horizontal layer of waters is 10⁻³ Nm⁻² .
Velocity of water = 18km/hr.
To express in m/s, we multiply with (1000/3600) to the value in km/hr.
[1 km = 1000m and 1 hr = 3600s].
So, velocity = 18×10/36 = 5m/s
The coefficient of viscosity of water is 10⁻² Poise
= 10⁻²/10 = 10⁻³ Nsm⁻². [1 Poise = 0.1 Nsm⁻².]
Shear stress is given as :
Shear stress = (Coeffecient of viscosity)×(Velocity/Depth)
Coeffecient of viscosity = 10⁻³ Nsm⁻²
Velocity = 5m/s
Depth = 5m.
Putting these values, we get
Shear stress = 10⁻³ × (5/5) Nm⁻²
= 10⁻³ Nm⁻²
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