Wave Mechanics Question 678
Question: A car is moving towards a high cliff. The car driver sounds a horn of frequency $ f $ . The reflected sound heard by the driver has as frequency $ 2f $ . If v be the velocity of sound, then the velocity of the car, in the same velocity units, will be
Options:
A) $ v/2 $
B) $ v/\sqrt{2} $
C) $ v/3 $
D) $ v/4 $
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Answer:
Correct Answer: C
Solution:
[c] Let f? be the frequency of sound heard by cliff
$ \
Therefore ,f’=\frac{vf}{v-v _{c}} $ ……. (1) Now for the reflected wave cliff, acts as a source
$ \
Therefore 2f’=\frac{f’(v+v _{c})}{v} $ …… (2) $ 2f=\frac{(v+v _{c})f}{v-v _{c}}\Rightarrow 2v-2,v _{c}=v+v _{c} $ or $ \frac{v}{3}=v _{c} $
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