Answer:
(I). The effective cross sectional area of the capillaries is 0.188 m².
(II). The approximate number of capillaries is 
Explanation:
Given that,
Radius of aorta = 10 mm
Speed = 300 mm/s
Radius of capillary 
Speed of blood 
(I). We need to calculate the effective cross sectional area of the capillaries
Using continuity equation

Where. v₁ = speed of blood in capillarity
A₂ = area of cross section of aorta
v₂ =speed of blood in aorta
Put the value into the formula



(II). We need to calculate the approximate number of capillaries
Using formula of area of cross section


Put the value into the formula


Hence, (I). The effective cross sectional area of the capillaries is 0.188 m².
(II). The approximate number of capillaries is 