Question

The net force exerted by fluid on moving plate is

• A. $0.6N$ backwards
• B. $0.6N$ forward
• C. $0.2N$ backwards
• D. $0.2N$ forward

Answer 1

The correct option is A $0.6N$ backwards

We know force $F=a\mu \frac{dv}{dy}$

a=cross section area=$0.01m^{2}v=1m/s$

force due to viscous force and upper plate when y$$ =4cm$

$F_1=a\mu \frac{\Delta v}{\Delta Y}=0.8\times 0.01\frac{1}{0.04}=.2N$

force due to viscous force and upper plate when $y=2cm$

$F_2=a\mu \frac{\Delta v}{\Delta Y}=0.8\times 0.01\frac{1}{0.02}=.4N$

Total force =$F_1+F_2=0.6N$ in backward direction.