(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

During a hurricane, a 1,200 Hz warning siren

on the town hall sounds. The wind is blowing

at 55 m/s in a direction from the siren toward

a person 1 km away. With what frequency does

the sound wave reach the person? (The speed of

sound in air is 330 m/s.)

(A) 1,000 Hz

(B) 1,030 Hz

(C) 1,200 Hz

(D) 1,400 Hz

(E) 1,440 Hz

2. Relevant equations

[tex]f = \left( \frac{c + v_r}{c + v_{s}} \right) f_0 \,[/tex]

C is the velocity of waves in the medium;

Vr is the velocity of the receiver relative to the medium; positive if the receiver is moving towards the source;

Vs is the velocity of the source relative to the medium; positive if the source is moving away from the receiver.

3. The attempt at a solution

Stop me at any point if I'm wrong:

C would be 330 m/s. Vr would be 55, and Vs would be 0?

I try plugging this into the formula, and I always ~1030 Hz, but the answer key (this is from a practice GRE) says that the answer is 1200 Hz. How do they get this answer?

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# Homework Help: The observed frequency of a 1,200 Hz wave

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