Question

A long cylindrical rod of radius $R_1$ is placed co-axially inside a cylindrical tube of radius $R_2(>R_1)$ filled withviscous liquid and pulled along the axis with a constant velocity. In steady state the velocity gradient $\left(\frac{dv}{dr}\right)$ depends on the distance from the common axis 'r' as proportional to

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

$f=\eta A\frac{dv}{dx}=const\eta 2\pi rl\frac{dv}{dx}=const\frac{dv}{dx}\alpha \frac{1}{r}$