Question
A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 m/s. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take, velocity of sound in air = 330 m/s)
-
800 Hz
-
838 Hz
-
885 Hz
-
765 Hz
Solution
B.
838 Hz
The situation can be illustrated as follows:
Frequency of sound that the observer hear in the echo reflected from the cliff is given by,f' =
where,
f = original frequency of source
v= velocity of the sound
vs = velocity of the source
So,
f = original frequency of source
v= velocity of the sound
vs = velocity of the source
So,
