Question

The velocity of water in river is 180 km h-' near the
surface. If the river is 5 m deep, then the Shearing
stress between the surface layer and the bottom layer
is (coefficient of viscosity of water, n = 10-3 Pa s)
(a) 10-2 Nm-2
(b) 10-3 Nm-2
(c) 10-4 Nm-2
(d) 10-5 Nm-2​

Answer 1

Answer:

As the velocity of water at the bottom of the river is zero,

dv=18kmh

−1

=18×

18

5

=5ms

−1

Also, dx=5m, η=10

−3

Pas

Force of viscosity, F=ηA

dx

dv

∴ Shearing stress, =

A

F

=η

dx

dv

=

5

10

−3

×5

=10

−3

Nm

−2