A siren emitting a sound of frequency 1000 Hz moves away from you towards a cliff at a speed of 10 m/s. (a) What is the frequency of the sound you hear coming directly from the siren ? (b) What is the frequency of the sound you hear reflected off the cliff (c) What beat frequency would you hear ? Take the speed of sound in air as, 330 m/s.

A siren emitting a sound of frequency 1000 Hz moves away from you towa

1.	A siren emitting a sound of frequency 1000 Hz moves away from you towards a cliff at a speed of 10 m/s. (a) What is the frequency of the sound you hear coming directly from the siren ? (b) What is the frequency of the sound you hear reflected off the cliff (c) What beat frequency would you hear ? Take the speed of sound in air as, 330 m/s.
Answer» Solution :The situation is as shown in figure. (a) FREQUENCY ofsound reaching DIRECTLY to us (by S) `f_1 (v/(v +v_s)) f = (330/(330 +10)) (1000) = 970.6 Hz` (b) Frequecny of SOUND which is reflected of from the cliff is same as from S. `f_2 = (v/(v -v_s)) f = ((330)/(330 "" 10))(1000)` ` = 1031.3 Hz` (c ) Beat FREQUNCY `=f_2-f-1=60.7 Hz` (Too high to be heared as BEATS)

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