Water enters a smooth, horizontal tube with a speed of 4.00 m/s and emerges out of the tube with a speed of 36.0 m/s. Each end of the tube has a different cross-sectional radius. Which radius is smaller? The radius at the exit The radius at entry Correct. Since the volume flow rate remains constant, the speed of the water increases as the area decreases. Assume that the cross-sectional area of the tube is circular. What is the ratio of the entrance radius to the exit radius?