Question

The velocity of water in river is 5 m/s at the surface. The river is 5 m deep. What is viscous forces per unit area between horizontal layer of water? The viscosity of water is 10-3 poiseuille.​

Answer 1

Answer:

option d because the velocity of water is at 10 power 3 and river is in 5m deep

Answer 2

Given:

• the velocity of water in the river is 5m/s at the surface
• The viscosity of water is 10^-3
• The river is 5m deep

To find: what is viscous forces per unit area between a horizontal layer of water?

Explanation:

as we know that,

velocity at the bottom of the river will be zero,

Velocity gradient,

                           =  dv/dy

                           = 18×$10^{3}$/60×60×5

                           = 1$s^{-1}$

Now,

The viscous force,

                         F = ηA$\frac{dv}{dY}$  is tangential to the area

by using the formula of Shear stress,

                          = F/A

                          = η$\frac{dv}{dY}$

                          = $10^{-3}$×1

                          = $10^{-3}$ $\frac{N}{m^{2} }$

Hence the viscous force is $10^{-3}$ $\frac{N}{m^{2} }$