Calculating Frequency of Siren in Windy Conditions

In summary, the conversation discusses how to calculate the frequency heard by someone approaching a siren at a specific speed with wind blowing in different directions. The correct formula for this calculation is provided and the final frequencies for both scenarios are determined.
  • #1
pat666
709
0

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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  • #2
Check the formula.
 
  • #3
That formula is the one in my textbook for the observer moving and the source stationary
 
  • #4
hey, i really need some help with this if you know a different equation i should use?
 
  • #5
pat666 said:
hey, i really need some help with this if you know a different equation i should use?
The correct formula is

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

Velocity of sound will be depending on the direction of the wind.
 
  • #6
ok thanks i don't know how i missed the second f...thanks
 
  • #7
I get (i) 941Hz and (ii) 938Hz

Does this sound right?
 

1. How does wind affect the frequency of a siren?

Wind can affect the frequency of a siren in two ways - by changing the speed of sound and by altering the relative motion between the siren and the listener. Wind speeds can vary the speed of sound, causing a change in the perceived frequency of the siren. Additionally, if the wind is blowing toward or against the direction of the siren, it can either increase or decrease the frequency that the listener perceives.

2. What is the formula for calculating the frequency of a siren in windy conditions?

The formula for calculating the frequency of a siren in windy conditions is: f' = (v + vw) / (v + vs) * f, where f' is the perceived frequency, v is the speed of sound, vw is the wind speed, vs is the speed of the siren, and f is the actual frequency of the siren.

3. How does the direction of the wind affect the frequency of a siren?

The direction of the wind can affect the frequency of a siren by creating a relative motion between the siren and the listener. If the wind is blowing towards the listener, it will increase the perceived frequency, and if it is blowing away from the listener, it will decrease the perceived frequency. If the wind is blowing perpendicular to the direction of the siren, it will have no effect on the frequency.

4. What other factors can impact the frequency of a siren in windy conditions?

Other factors that can impact the frequency of a siren in windy conditions include the temperature, humidity, and altitude of the area. These factors can also affect the speed of sound and therefore, alter the perceived frequency of the siren.

5. Are there any tools or methods for accurately measuring the frequency of a siren in windy conditions?

Yes, there are tools and methods for accurately measuring the frequency of a siren in windy conditions. One method is to use a digital frequency meter, which can measure the frequency of a siren in real-time. Another method is to use a sound level meter, which can measure the sound pressure level of the siren and then calculate the frequency using the speed of sound in the given conditions.

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