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## Homework Statement

A parked car's alarm goes off, producing a sound at 961 Hz.

As you drive toward, pass, and drive away from this parked car, you observe a frequency change of 98 Hz. At what speed are you driving?

(Speed of sound is 343 m/s.)

## Homework Equations

[tex]f_o = f_s\left( 1-\frac{v_o}{v} \right)[/tex] (Observer moving away from source)

And possibly

[tex]f_o = f_s\left( 1+\frac{v_o}{v} \right)[/tex] (Observer moving towards source)

## The Attempt at a Solution

Interesting problem. Using the above formula for Doppler shift when an observer is moving away from a source, I was coming up with

[tex]f_o = 863\left( 1-\frac{v_o}{343 m/s} \right)[/tex]

which solves to 34.9781 m/s, an incorrect answer.

Any hints on what I'm doing wrong? I was wondering if two-stepping this and using both equations would get anywhere, but without knowing for sure what the observer's frequency would be on that half of the trip, I'm a bit unsure of things.

Thanks.

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