A sphere of radius 1 cm is moving through a vat of corn syrup, which has a viscosity of 1.4 Pa s. A force of 0.01 N is needed to keep it moving at a constant speed. What is the speed? You may assume that Stokes' law applies.
A) 3.8 cm s-1.
B) 26 cm s-1.
C) 23 cm s-1.
D) 12 cm s-1.
E) 6.8 cm s-1.ANS

Question

Quizplus · Accepted Answer

Using Stokes' law, the force is given by F = 6πηrv, where η is the viscosity, r is the radius, and v is the speed. Solving for v gives v = F / (6πηr) = 0.01 N / (6 * 1.4 Pa s * 0.01 m) = 0.0119 m/s or 1.19 cm/s, which is closest to option A (3.8 cm/s).

A Sphere of Radius 1 Cm Is Moving Through a Vat