posted by Stephanie .
A siren mounted on the roof of a firehouse emits sound at a frequency of 900 Hz. A steady wind is blowing with a speed of 15 m/s. Take the speed of sound in calm air to be 343 m/s.
(c) Firefighters are approaching the siren from various directions at 15.0
m/s. What frequency does a firefighter hear if he or she is approaching
from an upwind position, so that he or she is moving in the direction
in which the wind is blowing?
(d) What frequency does a firefighter hear if he or she is approaching from a downward position and moving against the wind?
I know that for part C the Observer is traveling at 0m/s with respect to the wind and for Part D the observer is moving at 30m/s with respect to the wind. I know that the speed for the source is 15m/s.
I need help figuring out why the source is traveling towards observer for part C and away for part C. I don't get the direction of the sound from the source. Basically I am having trouble with setting up the correct denominators.