Models of torpedoes are sometimes tested in a horizontal pipe of flowing water, much as a wind tunnel is used to test model airplanes. Consider a circular pipe of internal diameter 21 cm and a torpedo model aligned along the long axis of the pipe. The model has a 4.9 cm diameter and is to be tested with water flowing past it at 2.5 m/s.

With what speed must the water flow in the part of the pipe that is unconstricted by the model?