Question

Now the force exerted by the liquid on the plate is:

• A. 0.6 N
• B. 0.4/3 N
• C. 1.6/3N
• D. None

Answer 1

The correct option is A 0.6 N

There will be backward viscous force acting on both the sides, first from liquid above the plate, and second from liquid below the plate. In this case $dx$ for one side liquid is 2 cm and for another side liquid, $dx$ is 4cm. so we have $F_v={\left(\mu A\frac{dv}{dx}\right)}_1+{\left(\mu A\frac{dv}{dx}\right)}_2\Rightarrow F_v=0.8\times 0.01\times \frac{1}{0.02}+0.8\times 0.01\times \frac{1}{0.04}=0.6N$