A sound source emits frequency of 175 Hz when moving towards a rigid w...
Frequency of direct sound heared by observer
Wave length of reflected sound wave
No. of beats heared by person
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A sound source emits frequency of 175 Hz when moving towards a rigid w...
Solution:
Given:
Frequency of sound emitted by the source, f = 175 Hz
Velocity of the source towards the wall, Vs = 5 m/s
Velocity of the observer away from the wall, Vo = 5 m/s
Velocity of sound, v = 355 m/s
To find:
The number of beats per second heard by the observer
Explanation:
When a sound source moves towards a stationary observer, the frequency of the sound waves received by the observer is higher than the frequency emitted by the source. This is known as the Doppler effect. Similarly, when the observer moves away from the sound source, the frequency of the sound waves received by the observer is lower than the frequency emitted by the source.
In this case, both the source and observer are moving, and the wall is stationary. The frequency of the sound waves received by the observer is given by the following formula:
f' = f (v + Vo) / (v - Vs)
Where, f' is the frequency received by the observer, f is the frequency emitted by the source, v is the velocity of sound, Vs is the velocity of the source towards the wall, and Vo is the velocity of the observer away from the wall.
Substituting the given values in the formula, we get:
f' = 175 (355 + 5) / (355 - 5)
f' = 180 Hz
Therefore, the frequency received by the observer is 180 Hz.
Now, the number of beats heard per second is given by the difference between the frequency received and the frequency emitted by the source. That is,
Number of beats per second = |f' - f|
Substituting the given values, we get:
Number of beats per second = |180 - 175|
Number of beats per second = 5
Therefore, the number of beats heard per second by the observer is 5.
Conclusion:
Hence, the correct answer is 5.
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