Question

I don't understand why for a) they are using 12pinDv, where is the 12 coming from?

7: Imagine a bacterium which is a sphere 10 m in diameter. It swims through water (which has a density of 1000 kg/m3 and a viscosity of η-8.90 × 10 Ns/m2) at a speed of 3x105 m/s. a. What is the magnitude of the frictional force acting on this bacterium? b. Estimate the mass of this bacterium c. If the bacterium suddenly stops swimming forward and allows friction to slow it to a halt, how far will it travel before coming to rest? a: We're now very much in the small/slow regime of friction. Here we have: F,-12πηDv-12n * 8.90x 10-4 Ns/m2 * 10.5 m * 3x10-5 m/s-1x10-11 N

Answer 1

Yes u r correct ,Here should not be 12 ,12 is written wrong.

According to stroker law it should be F=6π(eta)rV =3π(eta)Dv.

Where

r is radius .

D is diameter.

R=D/2