A) \[\frac{v}{\sqrt{2}}\]
B) \[\frac{v}{3}\]
C) \[\frac{v}{4}\]
D) \[\frac{v}{2}\]
Correct Answer: B
Solution :
When the sound is reflected from the cliff, it approaches the driver of the car. Therefore, the driver acts as an observer and both the source(car) and observer are moving. |
Hence, apparent frequency heard by the observer (driver) is given by |
\[f'=f\left( \frac{v+{{v}_{o}}}{v-{{v}_{s}}} \right)\] (i) |
where\[v=\] velocity of sound, |
\[{{v}_{o}}=\] velocity of car \[={{v}_{s}}\] |
Thus, Eq. (i) becomes |
\[\therefore \] \[2f=f\left( \frac{v+{{v}_{o}}}{v-{{v}_{o}}} \right)\] |
or \[2v-2{{v}_{o}}=v+{{v}_{o}}\] |
or \[3{{v}_{o}}=v\] |
or \[{{v}_{o}}=\frac{v}{3}\] |
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