Question

Spherical balls of radius $R$ are failing in a viscous fluid of viscosity $\eta$ with a velocity $v$. The retarding viscous force acting on the spherical ball is

• A. directly proportional to $R$ but inversely proportional to $v$.
• B. directly proportional to both radius $R$ and velocity $v$.
• C. inversely proportional to both radius $R$ and velocity $v$.
• D. inversely proportional to $R$ but inversely proportional to $v$.

Answer 1

The correct option is B directly proportional to both radius $R$ and velocity $v$.

According to stoke's law

$F=6\pi r\eta v\to \left(1\right)$

$F=$ viscous drag force

$r=$ radius of sphere

$\eta =$ viscosity of fluid

$v=$ velocity of sphere

From equation $\left(1\right)$ wecan so that $F\alpha R\&V$