What is the observed frequency of a siren with a frequency of

440 Hz moving towards you at 50 m/s? The speed of sound is

330 m/s.

Answer: The observed frequency is 518.6 Hz

Explanation:

By the Doppler Effect, we know that:

f' = ((v + v0) / (v - vs)) * f

where f' is the perceived frequency.

v is the velocity of the wave, in this case 330m/s

v0 is the velocity of the receptor, in this case 0m/s

vs is the velocity of the source, in this case - 50m/s (the minus sign is because it is coming thowards us)

f is the original frequency, f = 440hz.

then we have:

f' = 440hz * (330m/s) / (330m/s - 50m/s) = 518.6 Hz