Frequency of Horn: Solving Doppler Equation

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Homework Help Overview

The discussion revolves around the application of the Doppler effect in sound, specifically in the context of two trains moving relative to each other and the frequency of a horn being detected. The original poster presents two parts of a problem involving sound frequency detection based on the velocities of the trains.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to calculate the detected frequency using the Doppler equation for both scenarios involving stationary and moving trains. Some participants question the relative velocities and suggest considering the combined speed of both trains moving away from each other.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the velocities involved. There is an indication of productive direction as participants provide feedback on the calculations and logic presented, but no explicit consensus has been reached regarding the correct answer.

Contextual Notes

Participants are navigating the complexities of relative motion and the Doppler effect, with some uncertainty about how to properly apply the velocities in the equation. The original poster has received feedback but is still seeking clarification on the correct approach.

European Sens
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There are two questions here:

1st is...

The velocity of sound in air is 343 m/s. A train moving away from a detector at 29 m/s blows a 350 Hz horn. What frequency is detected by a stationary train?

I got the correct answer of 322.7 using dopplers equation.

Now part 2 is...

What frequency is detected by a train moving away from the first train at a speed of 15.6 m/s?

Plugging in ---->

f' = [350*343] / [343+15.6] = 334.77

It seems correct to me, but when I submitted my answer online I was incorrect.

Please help! Thanks!
 
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Try and imagine how fast train number two is moving away from train number one i.e. work out train number one's velocity relative to train number two and use that in the equation.
 
well train # 1 is going 29 m/s and train # 2 is going 15.6 m/s in opposite directions... that I know.

So do I add 29 + 15.6 to get 44.6 m/s away from each other...

which when plugged in is:
f' = [350*343] / [343+44.6] = 309.72


Please advice. Thank you.
 
Does my logic seem correct. Please lead me in the right direction. Thanks once again.
 
Yes that looks right, is it not the right answer?
 

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