Question

A Spherical ball of radius $1 \,mm$ and density $10.5\, g / cc$ is dropped in glycerine of coefficient of viscosity $9.8$ poise and density $1.5 \,g / cc$ Viscous force on the ball when it attains constant velocity is $3696 \times 10^{-x} N$. The value of $x$ is_______.
(Given, $g=9.8 \,m / s ^2$ and $\pi=\frac{22}{9}$ )

Answer 1

The correct answer is 7.
$F_v​=(mg−F_B​)(∵a=0)$

$=Vσ_b\,​g−Vρ_ℓ​\,g$

$=Vg(σ_b​−ρ_ℓ​)$

$=\frac4{3}​π(10^{−3})^3×9.8(10.5−1.5)×10^3$

$=3696×10^{−7}N$

$So , \,\,x=7$