Calculating Frequency of Siren in Windy Conditions

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Homework Help Overview

The problem involves calculating the frequency of a siren under the influence of wind conditions. The original poster presents a scenario where a siren emits a frequency of 900 Hz, with wind affecting the speed of sound as perceived by an observer moving towards the source.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to apply a formula for frequency adjustment based on relative velocity but expresses uncertainty about their calculations and the correct application of the formula. Some participants question the formula used and suggest checking its correctness. Others inquire about alternative equations that might be applicable.

Discussion Status

The discussion includes attempts to clarify the correct formula and its application. Some participants have provided calculations for the frequency under different wind conditions, but there is no explicit consensus on the correctness of these values. The conversation remains open for further exploration of the problem.

Contextual Notes

Participants note that the velocity of sound is influenced by the direction of the wind, which is a critical aspect of the problem. There is also an indication of confusion regarding the correct formula to use, highlighting potential gaps in understanding the underlying concepts.

pat666
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Homework Statement



(a) A siren emits a frequency of 900 Hz. Wind is blowing at a steady speed of 15.0 ms-1. The speed of sound in calm air is 343 ms-1. What is the frequency heard by someone approaching at 15.0 ms¹,

(i) when the wind blows from the person to the siren,
(ii) when the wind blows from the siren to the person?

Homework Equations



f'=(1+v_o/v)

The Attempt at a Solution



i figured out the relative velocity of the sound (for i 343-15) and then subbed into the formula which became 1+15/328=1.04573HZ. I'm pretty sure this isn't right because the frequency should get higher but mine inst even close... also i didnt use the given frequency at all?
 
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Check the formula.
 
That formula is the one in my textbook for the observer moving and the source stationary
 
hey, i really need some help with this if you know a different equation i should use?
 
pat666 said:
hey, i really need some help with this if you know a different equation i should use?
The correct formula is

f' = [1 + \frac{v_o}{v}]f

Velocity of sound will be depending on the direction of the wind.
 
ok thanks i don't know how i missed the second f...thanks
 
I get (i) 941Hz and (ii) 938Hz

Does this sound right?
 

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