Spherical balls of radius R are falling in a viscous fluid of viscosity h with a velocity v. The retarding viscous force acting on the spherical ball is :

Options

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

Answer

D

Explanation

According to Stoke.s law
`F=6etaRv`
`thereforeFpropR` and `Fpropv`
So the correct choice is (d).