Question

the novel coronavirus is a spherical particle of outer diameter 120 nm, while streptococcus bacteria are 1.8

?

μ

m in diameter. The virus is also found to be slightly more dense than the bacteria, with the density of coronavirus being 1.1 kg/L and that of strep being 1.1 kg/L. During an infection, both are found in the bloodstream (blood density is 1.0 kg/L; blood viscosity is 3.5*10^-3 pa

(a) A sample of blood containing streptococcus is placed in a centrifuge and spun at 18,000 revolutions per minute (RPM). Under these conditions, it is found that the bacteria sediment with a terminal speed of 0.5 mm/s. What would be the sedimenting terminal speed of coronavirus under the same conditions?

(b) What is the Reynolds number for the bacteria as it sediments in the centrifuge?

Re =

(c) Once the sample of coronavirus has been fully sedimented it is left in the vial for a few days. It is found that at a position 5 mm above the bottom of the vial the concentration of the virus particles is 43% of the concentration at the bottom of the vial. What is the relative concentration at a position 13 mm above the bottom of the vial?

(give your answer as a percent)

Answer 1