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 in same direction. Hence, apparent frequency heard \[f=f\left( \frac{v+{{v}_{o}}}{v-{{v}_{s}}} \right)\] where v = velocity of sound, \[{{v}_{o}}=\] velocity of car \[={{v}_{s}}\] \[\therefore \] \[2f=f\left( \frac{v+{{v}_{o}}}{v-{{v}_{o}}} \right)\] \[\Rightarrow \] \[2v-2{{v}_{o}}=v+{{v}_{o}}\] \[\Rightarrow \] \[3{{v}_{o}}=v\] \[\Rightarrow \] \[{{v}_{o}}=\frac{v}{3}\]
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