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  4. A car sounding its horn at 480 Hz moves towards a high wall at a speed of 20 ms−1 . If the speed of sound is 340 ms−1 , the frequency of the reflected sound heard by the girl sitting in the car will be closest to

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Q. A car sounding its horn at $ 480\, Hz $ moves towards a high wall at a speed of $ 20\, ms^{−1} $ . If the speed of sound is $ 340 \,ms^{−1} $ , the frequency of the reflected sound heard by the girl sitting in the car will be closest to

UPSEEUPSEE 2009Waves

Solution:

The frequency of reflected sound heard by the girl,
$n^{'} =n\left[\frac{v-\left(-v_{o}\right)}{v-v_{s}}\right]=n\left[\frac{v+v_{o}}{v-v_{s}}\right] $
$=480\left[\frac{340+20}{340-20}\right]=540 \,Hz$