Doppler Effect - Question

1. The problem statement, all variables and given/known data

An ambulance with a siren emitting a whine at 1530 Hz overtakes and passes a cyclist pedaling a bike at 2.22 m/s. After being passed, the cyclist hears a frequency of 1519 Hz. How fast is the ambulance moving? (Take the speed of sound in air to be 343 m/s.)


2. Relevant equations

http://img15.imageshack.us/img15/3340/equationx.jpg [Broken]

3. The attempt at a solution

Since both the cyclist and the ambulance is moving it is slightly confusing for me.

I have tried this question multiple times but am unable to get the right answer.

I tried to the question where the ambulance is moving and the cyclist is stationary and then just add the velocity of the cyclist onto the velocity I get for the ambulance.

This is what i tried :

http://img18.imageshack.us/img18/426/answer.jpg [Broken]

It is wrong but if someone is able to tell me what I did wrong that would be great.

Cheers
1. The problem statement, all variables and given/known data



2. Relevant equations



3. The attempt at a solution
 
Last edited by a moderator:

Delphi51

Homework Helper
3,407
10
There is an error in the formula you are using. According to my text
it should be f' = f*v/(u + v)
where v is the speed of sound and u the speed at which the source is moving away from the observer. It comes out to 2.48, to which the 2.2 must be added.
 
So is the speed of the ambulance would be 2.48 + 2.2 = 4.68 m/s ??

Nice its right :D

Thanks
 

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