The velocity of water in a rier is `18kmh^-1` near the surface. If the river is 5 m deepm, find the shearing stress between the horizontal lyers of water. The coefficient of viscosity of water `=10^-2 poise.

Options

A. `10 ^(-1) N//m^(2)`
B. `10 ^(-2) N//m^(2)`
C. `10 ^(-3) N//m^(2)`
D. `10 ^(-4) N//m ^(2)`

Answer

B

Explanation

`eta =10 ^(-2)` poise
` v = 18 km//h (18000)/(3600) =5 m//s`
`l = 5m ` Strain rate `= v/l`
Coefficient of viscosity, `eta = ("shering stress")/("strain rate")`
`therefore` Shearing stress `=eta xx` strain rate `= 10 ^(-2) xx 5/5 = 10 ^(-2) Nm ^(-2)`