(a)
Given:
Diameter of the artery
Viscosity of the blood
Density of the blood
Then the largest average velocity of the blood flow is given as,
Substitute the values.
Then, the largest velocity of the flow of the blood is
(b)
Dissipative forces are the forces in which energy is lost from the system even in motion. If dissipative forces are present in the veins blood flow, then some of the force is spent against dissipative forces due to pressure difference, which causes pressure difference to become larger.
Dissipative forces are more important with increase in fluid velocity due to turbulence, which overcomes the damping effect of fluid viscocity.