The velocity of water in a river is 18 km h - 1 near the surface. If the river is 5 m deep, find the shearing stress between the horizontal layers of water. The coefficient of viscosity of water = 10 - 2 poise .

Step-by-step solution

Viscous force = F v = - η A · d v d h = 10 - 3 × A × 18 × 1000 3600 × 5   ,       η = 10 - 2   poise η = 10 - 3   decapoise   mks ∴   F v A = 1 8 5 × 3 6 0 0 = 1 2 0 0 × 5 ⇒ F v A = 1 0 - 3   N   m - 2