Question

A layer of glycerine of thickness 1 mm is enclosed between a big plate and another plane of area ${10}^{-2}{m}^2$. If the coefficient of viscosity of glycerine is $1kg/\left(ms\right)$, then the force in Newton required to move the plate with a velocity of 0.07 m/s will be:

• A. 7
• B. 0.7
• C. 70
• D. 0.07

Answer 1

The correct option is B 0.7

The force required should overcome the shear resistance due to the viscosity of the liquid, the shear force is given by

$F_s=\mu \frac{du}{dy}A$

$=1\times \frac{0.07}{1\times {10}^{-3}}\times {10}^{-2}=0.7N$