Question

Calculate the force required to move a flat glass plate of area 10cm square with uniform velocity of 1/s over the surface of liquid 2mm thick, if coefficient of viscosity of liquid is 2 pa.s​

Answer 1

.hence the answer is 0.2325N

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Answer 2

Given: A flat glass plate of area 10 cm² with uniform velocity of 1 ms⁻¹ over the surface of liquid 2 mm thick and coefficient of viscosity of the liquid is 2 Pa-s.

To find: The force required.

Solution:

• When a fluid flows, there exists a relative motion between the layers of the fluid.
• Internal force acts that destroy this relative motion. This force is called viscous force.
• The viscous force is given by the formula,

        $F = - n A \frac{dv}{dx}$

• Here, A is the area of the layer, $\frac{dv}{dx}$ is the velocity gradient and η is the coefficient of viscosity of the fluid.

• The area is given as 10 cm², which is equal to 0.001 m².
• The thickness is given as 2 mm, which is equal to 0.002 m.$F = - (2) (0.001 m^{2}) \frac{1ms^{-1}}{0.002 m}$

            $= - 1 N$

Therefore, the force required is -1 N.