Final answer:
Flow rate and velocity are related by Q = Au. The velocity of an incompressible fluid increases when the cross-sectional area of the pipe decreases.
Step-by-step explanation:
Flow rate and velocity are related by Q = Au where A is the cross-sectional area of the flow and v is its average velocity. The equation of continuity states that for an incompressible fluid, the mass flowing into a pipe must equal the mass flowing out of the pipe.
In a horizontal flow of an incompressible fluid, the cross-sectional area of the pipe decreases, which leads to an increase in velocity to maintain the continuity of flow. Therefore, the velocity of the fluid increases when the cross-sectional area decreases.