Question

7. An ambulance is approaching you at 30 m/s, sounding its siren at a frequency of 750 Hz? If the speed of sound is 345 m/s, what frequency do you observe? Assume your velocity is 0 m/s

Answer 1

Answer:

816 Hz

Explanation:

To find the velocity observed, we can doppler effect's formula. It is given by -

• $\sf f' = f_{o} \dfrac{v + v_{source}}{v + v_{observer}}$

Where,

• f' is the observed frequency.
• $\sf f_{o}$ is frequency of the source.
• v is speed of sound
• $\sf v_{source}$ is velocity of the source
• $\sf v_{observer}$ is the velocity of the observer.

We are given that An ambulance is approaching you at 30 m/s, sounding its siren at a frequency of 750 Hz. The speed of sound is 345 m/s.

Here,

• Speed of sound = 345 m/s
• $\sf v_{source}$ is 30 m/s
• $\sf v_{observer}$ is 0 m/s since the observer is at rest.
• $\sf f_{o}$ is 750 Hz

Substitute the given values in the above formula,

$\sf f' = 750 \dfrac{345 + 30 }{345 + 0}$

$\sf f' = 750 \times \dfrac{375 }{345 }$

$\sf f' = 750 \times 1.087$

$\sf f' \approx 816 \: Hz$

• Hence, the observed frequency is 816 Hz