Doppler Effect of a blown whistle

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Homework Help Overview

The problem involves a whistle with a frequency of 500 Hz that revolves in a horizontal circle, and the listener's perception of frequency due to the Doppler effect. The setup includes a string of length 1.2 m and a rotation speed of 400 revolutions per minute, with the speed of sound given as 340 m/s.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the application of the Doppler effect at different points in the whistle's circular path, questioning how to convert the rotation speed from revolutions per minute and how to relate the string length to the radius of the circle.

Discussion Status

Some participants have offered guidance on calculating velocity and converting units, while others are exploring the relationship between the string length and the radius of the circular motion. Multiple interpretations of the problem setup are being discussed.

Contextual Notes

There is uncertainty regarding the use of the string length in calculations and how to properly apply the Doppler effect in this context. Participants are navigating through the problem without a clear consensus on the approach.

lha08
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Homework Statement


A whistle of frequency 500 Hz tied to the end of a string of length 1.2 m revolves at 400 rev/min. A listener standing some distance away in the plane of rotation hears frequencies in the range ____?
(speed of sound=340 m/s)
a) 436 to 586
b) 426 to 574
c) 426 to 584
d) 436 to 674


Homework Equations





The Attempt at a Solution


I'm not really sure how to approach this particular problem...i'm lost especially for the units and what to do with the string...thanks
 
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when the whistle is moving in a horizontal circle, at two points on the circle the whistle is moving either towards the observer or away from him. Apply Doppler effect to find the frequencies.
 
rl.bhat said:
when the whistle is moving in a horizontal circle, at two points on the circle the whistle is moving either towards the observer or away from him. Apply Doppler effect to find the frequencies.

okay i understand that part, but how do i convert 400 rev/min and for the length of the string do i use C=2(pi)radius and solve for r?
 
Last edited:
Velocity v = 2*pi*n*r where n is the number revolution per second.
 
rl.bhat said:
Velocity v = 2*pi*n*r where n is the number revolution per second.

but how do i solve for the radius using the length of the string?
 
lha08 said:
but how do i solve for the radius using the length of the string?
Length of the string itself is the radius.
 

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