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, and
(ii) when the wind blows from the siren to the person?
f^'=f/((1-v_s/v) ) source approaching
The Attempt at a Solution
for i) i figured that since the sound is no longer in calm air that the velocity v_s would be 343-15=328m/s, and v would be 15m/s.. so that comes out to -.1916Hz????????????? frequency cant be negative can it? i imagine ii) is the same method??? please help