A car is moving away from a stationary listener with a velocity of 20 m/s. if the horn is sounding at frequency 512 Hz, calculate the change in pitch of the sound received by the listener. (Velocity of sound in air = 330 m/s).
1 Answer
Solution:
Given,
Velocity of source (us) = 20 m/s
Velocity of an observer (uo) = 0
Frequency of the horn 9f) = 512 Hz
Velocity of the sound in the air (v) = 330 m/s
Change in the pitch = ?
Now, using the Doppler's effect formula, we have
\(f_1'=\frac{v\pm u_o}{v\pm u_s}\times f\)
In the condition, when the observer approaches the source, we have,
\(f'=\frac v{v+u_s}\times f=\frac{330}{330+20}\times512\)
∴ f' = 482.74 Hz
Hence, the change in pitch = f - f' = (512 - 482.7) Hz = 29.26 Hz
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