A large wooden plate of area 10m^2 float...

A large wooden plate of area `10m^2` floating on the surface of river is made to move horizontally wilth a speed of `2ms^-1` by applying a tangential force. If the river is 1m deep and the water contact with the bed is stationary, find the tangential force needed to keep the plate moving. Coefficient of viscosity of water at the temperature of the river `=10^-2 poise.`

velocity gradient is `2s^(-1)`

velocity gradient is `1s^(-1)`

force required to keep the plate moving with constant speed is 0.02N

force required to keep the plate moving with constant speed is 0.01N

Verified by Experts

The correct Answer is:

A, C

Velocity gradient `=(Delta v)/(Deltah)=(2m//s)/(1m)=2s^(-1)`
`F=eta A(Delta v)/(Deltah)=(10^(-3))(10)(2)`
`=0.02N`.

A boat with base area 8m ^(2) floating on the surface of a still river is intended to move with a constant speed of 2 m/s by the application of a horizontal force. If the river bed is 2m deep find the force needed, (assuming a constant velocity gradient) Coefficient of viscosity of water is 0.90 xx 10 ^(-2) poise.

729 dyne

620 dyne

520 dyne

360 dyne

`2.25xx10^(-2)N`

`2.25xx10^(-1)N`

`2.25xx10^(-3)N`

`2.25xx10^(-4)N`

`10^(-1)N//m^2`

`10^(-2)N//m^2`

`10^(-3)N//m^2`

`10^(-4)N//m^2`