The radius of the aorta is about 1.0 cm, and the blood flowing through it has a speed of about 30 cm/s.  (a) Calculate the speed of the blood in the  capillaries, of which there are billions, each of diameter approximately equal to 8 x 10 ^{– 4} cm, resulting in a total capillary cross sectional area of about 2,000 cm².  (b) The density of blood is about 1,060 kg/m³.  What is the mass flow rate of blood through the aorta?

Answers: (a) 0.47 mm/s    (b) 0.10 kg/s