Question

A spherical ball of radius $5\text{mm}$ flowing through the glycerin as shown in figure. The velocity of ball at a particular instant is $0.6\text{m/s}$. Find the drag force on the ball due to the fluid. Assume that Stoke's law is valid. (Take viscosity of glycerine as $0.950\text{kg/m-s}$)

• A. $0.026\text{N}$
• B. $0.088\text{N}$
• C. $0.107\text{N}$
• D. $0.053\text{N}$

Answer 1

The correct option is D $0.053\text{N}$

Given, radius of spherical ball, $r=5\text{mm}$
Viscosity of glycerine, $\mu =0.950\text{kg/m-s}$
Velocity of ball, $v=0.6\text{m/s}$
Now, by Stoke's law,
Drag force is given by
$F_D=6\pi \mu rv$
$\Rightarrow F_D=6\times \pi \times 0.950\times 5\times {10}^{-3}\times 0.6$
$\Rightarrow F_D=0.053\text{N}$