Doppler Effect of a security alarm

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SUMMARY

The discussion centers on calculating the speed of a vehicle based on the Doppler Effect observed from a security alarm emitting a frequency of 735 Hz. The speed of sound is given as 343 m/s, and the observed frequency change is 78.4 Hz. The correct speed of the vehicle is determined to be 36 m/s, which accounts for the increase in frequency as the vehicle approaches the stationary car and the decrease as it moves away. A miscalculation was noted, indicating that the initial answer provided was twice the correct value.

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Homework Statement



The security alarm on a parked car goes off and produces a frequency of 735 Hz. The speed of sound is 343 m/s. As you drive toward this parked car, pass it, and drive away, you observe the frequency to change by 78.4 Hz. At what speed are you driving?

2. The attempt at a solution

Is it correct : ??

fo=735
f=735+78,4=813,4Hz

f=fo*[(V+Vo)/V]
v=36m/s
 
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As you drive towards the stationary car the alarm frequncy is higher due to your movement.
As you go away from it the frequency is lower.
78.4Hz is the difference between these two frequencies.

Without actually doing the working it looks like you've found an answer twice the correct one.
 

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