The velocity profile in a fluid stream is approximated using a three-part model, where the velocity is 1.6 m/s in 15 percent of the cross-sectional area, 3.2 m/s in 35 percent of the area, and 4.5 m/s in the rest of the area. 

(a) How much does the total momentum of the fluid differ from the product of the mass flow rate and the average velocity? 

(b) Can you think of a situation where there is a velocity profile in the flow stream and the momentum flow is exactly equal to the mass flow times the average velocity?