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

η = 10 − 2 poise = 10 - 3 Pa   s v = 18   km   h - 1 = 18000 3600 = 5   m   s - 1 d = 5   m Viscous force F = η A d v d x F A = η d v d x = 10 - 3 × 5 5 = 10 - 3  N  m - 2