Why Does Pressure Drop in a Constricted Bronchus?

[frenchy7322]

When a person inhales, air moces down the bronchus (windpipe) at 15 cm/s. The average flow speed of the air doubles through a constriction in the bronchus. Assuming incompressible flow, determine the pressure drop in the constriction.

This confuses me as I thought if you constrict a passage (e.g artery due to cholesterol) you get a higher pressue. This question is asking for the pressure drop??

As for equation... P = F/A? not real sure at all, someone please help to get the ball rolling :)

 

[Shooting Star]

Think of water instead of air, since in the problem the fluid is given as incompressible. If the fluid is to be kept flowing without accumulating anywhere, the speed has to increase in the narrow portions. But why would the fluid rush to the constricted portions if the pressure wasn't low there compared to where it's coming from?

Use Bernoulli's law without the gravity term.