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A car is moving towards a high cliff. Th...

A car is moving towards a high cliff. The driver sounds a horn of frequency f. The reflected sound heard by the driver has frequency 2f. If v is the velocity of sound, then the velocity of the car, in the same velocity units, will be

A

`v//sqrt(2)`

B

`v//3`

C

`v//4`

D

`v//2`

Text Solution

Verified by Experts

The correct Answer is:
B
Initially, the car is the source and at the cliff, one observes, `f.`.
`therefore f. =(v/(v-v_(s)))f`.
Now, cliff is source, it emits frequency `f.` and the obserer is now the driver who observes `f^(..)`.
`therefore f.. = [(v+v_(0))/v].` or `2f[(v+v_(0))/(v-v_(s))]f`
`rArr 2v -2v_(0) =v+v_(0) rArr v=v_(0) + 2v_(0)` [as `v_(s) =v_(0)]`
`rArr v_(0) =v/3`
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