Question

Suppose you're on a hot air balloon ride, carrying a buzzer that emits a sound of frequency f. If you accidentally drop the buzzer over the side while the balloon is rising at constant speed, what can you conclude about the sound you hear as the buzzer falls toward the ground?
A. the frequency remains the same, but the intensity decreases
B. the frequency decreases and the intensity increases
C. the frequency and intensity increase
D. the frequency decreases and the intensity decreases

Answer 1

Answer:

The correct answer is option 'd': The frequency decreases and the intensity of the sound decreases.

Explanation:

1) Effect on Frequency

According to Doppler's effect of sound we have

for a source of sound moving away from the observer the relation between the observed and the original frequency is given by

$f_{app}=\frac{c-v_{rec}}{c+v_{s}}\times f_{original}$

where

c = speed of sound in air

$v_{rec}$ is the velocity of observer of sound

$v_{s}$ is the velocity of source of sound

$f_{o}$ is the original frequency of sound

As we see the ratio is less than 1 thus the frequency of sound that the observer receives is less than that of source.

2) Effect on Intensity:

At a distance 'r' from source emitting a wave of Power 'P' is given by

$I=\frac{P}{4\pi r^{2}}$

As we see on increasing 'r' intensity of sound decreases.