Doppler effect

  • Thread starter Any Help
  • Start date
  • #1
79
2

Homework Statement


:
An ambulance has a siren of frequency 880 Hz. You are sitting at a stop light as the ambulance passes you, traveling at a constant 22 m/s. If the speed of sound is 343 m/s, what is the change in the frequency that you hear as the ambulance passes you?


  • A

    -53 Hz

  • wrong-icon.png


    B

    -60 Hz



  • C

    -56 Hz

  • correct-icon.png


    D

    -113 Hz



  • E

    -116 Hz
the correct Answer is D : -113 Hz


Homework Equations


CodeCogsEqn-4.gif

WHERE FL and vL are the frequency and velocity of sound heard by the personL
fs and vs are the frequency and velocity of sound emmited by the source


The Attempt at a Solution


using the equation we get FL=880x(343+0)/(343-22) therefore FL=940.3Hz
the difference is FL-Fs=940.3-880=60.311Hz
but its not correct.
the correct answer is -113Hz why???
 

Answers and Replies

  • #2
Doc Al
Mentor
44,993
1,266
What's the observed frequency when the ambulance is moving towards you? And then away from you?
 
  • #3
79
2
WhaF frequency when the ambulance is moving towards you? And then away from you?
1) when towards me it is FL1=Fs*v/(v-vs)=880*343/(343-22)=940 Hz
when moves away from me FL2=Fs*v/(v+vs)=880*343/(343+22)=827Hz
FL2-FL1=827-940=113 Hz
Ah okay thanksssss
 

Related Threads on Doppler effect

  • Last Post
Replies
3
Views
795
  • Last Post
Replies
1
Views
792
  • Last Post
Replies
1
Views
702
  • Last Post
Replies
0
Views
1K
  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
1
Views
662
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
6
Views
777
  • Last Post
Replies
2
Views
788
  • Last Post
Replies
7
Views
2K
Top