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  4. A whistle of frequency 1000 Hz is sounded on a car travelling towards a cliff with velocity of 18 ms -1 normal to the cliff. If c=330 ms -1, then the apparent frequency of the echo as heard by the car driver is nearly

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Q. A whistle of frequency $1000 \,Hz$ is sounded on a car travelling towards a cliff with velocity of $18\, ms ^{-1}$ normal to the cliff. If $c=330\, ms ^{-1}$, then the apparent frequency of the echo as heard by the car driver is nearly

BITSATBITSAT 2020

Solution:

By the concept of accoustic, the observer and source are moving towards each other, each with a velocity of $18\, ms ^{-1}$
$\therefore v'=\frac{330+18}{330-18} \times 1000 \approx 1115 \,Hz$