Calculating Pressure Drop in a Bronchial Constriction

[frenchy7322]

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

OK what confuses me is that I thought that if you decrease the width of a passage (e.g cholesterol in an artery) you increase pressure. However this asks for pressure DROP in constriction?

Equation I thought would be P = F/A, but not real sure at all.

Please help me get the ball rolling!

 

[luben]

To help you judge, let's compare this.
When there is a constriction in a pipe, the overall pressure in the WHOLE tube should be higher than that of a pipe with no constriction, given similar inlet flow speed. Now look at the tube with constriction, and compare the pressure at the inlet and at the constriction, the pressure at the constriction is always lower. It is this pressure difference that drives the air from inlet to the constriction! That phenomena is governed by the Bernoulli equation.