Question

What is the viscous drag acting on a sphere with a diameter of 16.2 mm falling through water at 2.3 ms^-1? Take the viscosity of the water to be 1.1 x 10^-3 Nsm^-2.

A 3.9 x 10^-4 N

B 7.7 x 10^-4 N

C 0.39 N

D 0.77 N

Answer 1

The viscous drag acting on a sphere is given by

$$F_d=6\pi\eta Rv$$

$$F_d=6*3.14*1.1*10^{-3}*8.1*10^{-3}*2.3\\ =3.9*10^{-4}\:\rm N$$

Answer: A