fluids question?

Answer the following question and explain your reasoning..A network of fine capillaries connects the arteries and the veins. The blood flows from the heart through large arteries, which subdivide and deliver blood to the capillary system. Each capillary is very small, about 10-6 m in radius, but there are so many of them that the total cross-section area through which the blood passes is about 0.2 m2 for the entire capillary system. This total area for the capillaries is greater than the cross-
section of a single vessel (such as the aorta) through which all blood flows. The average speed the blood moves through a capillary is a) faster than through the aorta.
b) slower than through the aorta.
c) the same speed as through the aorta.
c) any of these, depending upon the length of the aorta.
d) none of these
Answer:
b) slower than in the aorta.
mass flow rate = mass x velocity x flow area
since the mass flow rate is constant (blood isn't entering or leaving the body) the equation becomes
velocity a x flow area a = velocity c x flow area c
if flow area c is greater than flow area a, velocity c must be greater than velocity a

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b

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Slower. Length is a trivial factor compared to cross-sectional area in fluid flow.

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