The Doppler Effect Homework: Speed of Train from 940Hz to 915Hz

AI Thread Summary
The discussion centers on calculating the speed of a train using the Doppler Effect, where a stationary observer hears a frequency change from 940Hz to 915Hz as the train passes. The speed of sound in air is given as 343 m/s, and the relevant equation is provided for solving the problem. Participants express difficulty in obtaining the correct answer, with some reporting calculations yielding 9.4 m/s instead of the expected values listed. The potential answers range from 7.3 m/s to 42 m/s, but users are uncertain about their arithmetic or if they are missing a concept. The thread highlights the challenges faced in applying the Doppler Effect formula correctly.
san512
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Homework Statement


A train moving at a constant speed is passing a stationary observer on a platform. A flute player is playing a note with a frequency of 940Hz. after the flute has passed, the observer hears the sound frequency of 915Hz. What is the speed of the train? The speed of sound in air is 343m/s.

Homework Equations



Fo = Fs (1/(1+(Vs/V))

The Attempt at a Solution



Vs = ((Fs/Fo) - 1) * V

When i input the given information I keep getting the wrong answer. Is my arithmetic wrong or am I missing something completely?
 
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What is the given answer and what are you getting?
 
A) 7.3 m/s
B) 12 m/s
C) 21 m/s
D) 32 m/s
E) 42 m/s

I get 9.4 m/s
 
Same here unfortunately.
 
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