Consider a siren on top of a fire truck, where the truck is travelling at 35.0 m
ID: 3896741 • Letter: C
Question
Consider a siren on top of a fire truck, where the truck is travelling at 35.0 m/s on its way to a fire. the siren had a frequence of 1000 Hz, and give off 20.0 watts of acoustic power. the fire truck is moving and the air temeperature is 27 degress Celsius.
a) what is the speed of the sound waves leaving the siren on the fire truck?
b) what is the intensity of the sound waves produced by the siren 50.0 m away from the fire truck assuming the siren acts as a point source and the sound radiates equally in all directions?
c) what is the intensity level (decibels) of the sound 50.0 m away from the truck?
d) what frequency will a person hear from the siren if the person is stationary at an intersection as the fire truck approaches?
e) what frequency would a person in a car, traveling towards the fire truck hear?
Explanation / Answer
a. 331+.6*27=347.2m/s
b.I=P/R^2=8*10^-3
c.10log(I/Io)=99.03db
d.f=fo(c/c-Vs)=1112.1
e.f=fo((c+Vc)/(c-Vs))