physics multiple choice question

Question

For a small sphere of radius r moving through a viscous fluid, the drag force acting on the sphere is proportional to which of the following?

A. r³

B. r⁴

C. r²

D. r

Answer 1

The Viscous force is given by

F = 6∏* η* r* v ( Stoke's Law)

where ∏ = 3.14

η = coefficient of viscosity

r = radius

v = terminal velocity

SO answer D is correct