Doppler Effect

  • #1

Homework Statement


A stationary observer at a crosswalk hears an ambulance siren with an apparent frequency of
480 Hz when the ambulance is approaching. After the ambulance passes the apparent frequency is only 420 Hz. Find the speed of the ambulance. Assume v = 343 m/s for the speed of sound in air.


Homework Equations


source moving towards observer: f' = (vf)/(v - vs)
source moving away from observer: f' = (vf)/(v + vs)

The Attempt at a Solution


I am having trouble because I am not sure how to figure out what the frequency of the sound given off by the ambulance is. I tried using 450 since it is halfway between, and it gave me a close answer, but not the correct one. Any help would be much appreciated.

Thanks a lot
 

Answers and Replies

  • #2
tiny-tim
Science Advisor
Homework Helper
25,836
252
hi asdf12321asdf! :smile:
source moving towards observer: f' = (vf)/(v - vs)
source moving away from observer: f' = (vf)/(v + vs)

The Attempt at a Solution


I am having trouble because I am not sure how to figure out what the frequency of the sound given off by the ambulance is. I tried using 450 since it is halfway between, and it gave me a close answer, but not the correct one.

Quelle surprise!! :rofl:

c'mon … use some algebra! :wink:
 
  • #3
oh ok I figured it out thanks a lot
 

Related Threads on Doppler Effect

  • Last Post
Replies
1
Views
800
  • Last Post
Replies
3
Views
904
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
6
Views
1K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
2
Views
785
  • Last Post
Replies
1
Views
891
  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
12
Views
1K
Top