Final answer:
The question falls under high school level Physics and is about the fluid dynamics in the cardiovascular system. Without specific flow rate information, we cannot calculate the exact radius of a capillary, but we can assert that the radius is significantly smaller than that of the aorta, and there are many such capillaries to explain the decrease in blood speed.
Step-by-step explanation:
The question pertains to the area of Physics, specifically the branch dealing with fluid dynamics in the cardiovascular system. We are given that the aorta carries blood away from the heart at a speed of 38 cm/s with a radius of approximately 1.1 cm. As we know from the principle of conservation of mass (continuity equation), the product of the cross-sectional area of a vessel and the velocity of the fluid (blood in this case) must remain constant. Therefore, when blood reaches the much narrower capillaries, its speed dramatically decreases.
To find the radius of a capillary given the speed of blood within it, we can apply the continuity equation. However, we do not have enough information in the question to calculate the value directly, because we would need the flow rate or the total cross-sectional area of all the capillaries combined. We can, nonetheless, state that the capillaries have a much smaller radius than the aorta and that there are many capillaries to account for the slowed speed of blood, as this ensures a much larger total cross-sectional area.
Since we can compute the speed and flow rate in larger vessels quite easily, it illustrates the importance of the vast network of tiny capillaries in the human cardiovascular system.