Question

A large wooden plate of area 10 m floating on the surface of a
area 10 m floating on the surface of a river is made to move horizontally with a speed
of 2 m/s by applying a tangential force. If the river is 11
sung a tangential force. If the river is 1 m deep and the water in contact with the bed is
stationary, find the tangential force needed to keep the plate mou
e tangential force needed to keep the plate moving. Coefficient of viscosity of water at the
temperature of the river.= 10 poise.

Answer 1

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

Explanation:

Given data:

Area of wooden plate = 10 m^2

Speed "v"  = 2 m/s

Depth of river = 1 m

Coefficient of viscosity of water = 10^−2 poise

Solution:

Velocity gradient =Δv/Δh=2 m/s / 1m = 2 s−1

F = η AΔv / Δh

= (10^−3)(10)(2)

= =0.02 N.

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

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Answer 2

Answer:0.02N

Explanation:Area of wooden plate = 10 m^2

Speed "v"  = 2 m/s

Depth of river = 1 m

Coefficient of viscosity of water = 10^−2 poise

Solution:

Velocity gradient =Δv/Δh=2 m/s / 1m = 2 s−1

F = η AΔv / Δh

= (10^−3)(10)(2)

= =0.02 N.

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