physics continuity problem please help?

Question

The volume flow rate in an artery supplying the brain is 3.00 10-6 m3/s.

(a) If the radius of the artery is 4.90 10-3 m, determine the average blood speed.

(b) Find the average blood speed at a constriction in the artery if the constriction reduces the radius by a factor of 3. Assume that the volume flow rate is the same as that in part (a).

Answer 1

Volume flow rate = velocity *section
so velocity = 3.00*10^-6/(pi *4.9^2*10^-6 = 0.1249m/s
If the radius is reduced by a factor of 3 the section is reduced by a factor of 9 so the speed increases 9 fold
=1.1245 m/s