The typical diameter of an alveolus is 0.3 mm. The surface tension of water is about 70 dyne cm-1. The dyne is the unit of force in the cgs system: 1 g cm s-2. It is converted to N by multiplying by 10-3kg g-1x 10-2m cm-1 = 10-5 kg g-1 m cm -1. What is the pressure within this alveolus assuming no surfactant at mechanical equilibrium? Give the answer in Pascals (N m-2) and in mm Hg.

Atrain is traveling at 30.0 m/s relative to the ground in still air. the frequency of the note emitted by the train whistle is 262 hz. the speed of sound in air should be taken as 344 m/s. what frequency (f approach) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and approaching it? what frequency (f recede) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and receding from it?