Re: Doppler Effect Problem

[Robert Cohen <Robert.Cohen@PO-BOX.ESU.EDU>]

What is the speed of sound on a windy day?

____________________________________________
Robert Cohen; rcohen@po-box.esu.edu; 570-422-3428; http://www.esu.edu/~bbq
Physics, East Stroudsburg Univ., E. Stroudsburg, PA 18301

> -----Original Message-----
> From: Peter Schoch [mailto:pschoch@NAC.NET]
> Sent: Thursday, March 13, 2003 11:44 AM
> To: PHYS-L@lists.nau.edu
> Subject: Doppler Effect Problem
>
>
> I have a question regarding the Doppler Effect.  The following is the
> problem I'm trying to 'do':
>
> A car is chasing a UFO through still air.  The car is traveling at 30
> m/s toward the UFO, while the UFO is traveling at 100 m/s 
> away from the
> car.  The aliens are playing a note at 330 Hz.  What frequency do you,
> in the car, hear?
>
> Now, I worked this as f_heard = f_emit (v_air + 30)/(v_air + 
> 100) and I
> get an answer, assuming v_air =  343.
>
> However, I _thougth_ that I could also work this as the car being
> stationary and the UFO traveling away at 70 m/s using
>
> f_heard = f_emit (v_air) /( v_air + 70), again using v_air = 
> 343.  But,
> I don't get the same answer.
>
> What am I doing wrong; or more likely, what assumption have I made in
> the second case that is wrong?
>
> Thank you,
> Peter Schoch
> SCCC