The driver of a car travelling with speed 30 | vedclass

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(A) The problem involves the Doppler effect with a moving source and a moving observer (the driver).$1$. First,the sound from the horn travels to the

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$720$

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(A) The problem involves the Doppler effect with a moving source and a moving observer (the driver).$1$. First,the sound from the horn travels to the hill. The hill acts as a stationary observer receiving sound from a source (the car) moving towards it at $v_s = 30 \ m/s$. The frequency $n_1$ received by the hill is:$n_1 = n \left( \frac{v}{v - v_s} ight) = 600 \left( \frac{330}{330 - 30} ight) = 600 \left( \frac{330}{300} ight) = 660 \ Hz$.$2$. The hill reflects this sound,acting as a stationary source of frequency $n_1 = 660 \ Hz$. The driver (observer) is moving towards the hill at $v_o = 30 \ m/s$. The frequency $n'$ heard by the driver is:$n' = n_1 \left( \frac{v + v_o}{v} ight) = 660 \left( \frac{330 + 30}{330} ight) = 660 \left( \frac{360}{330} ight) = 2 	imes 360 = 720 \ Hz$.Alternatively,using the combined formula for a moving observer and source towards a stationary reflector:$n' = n \left( \frac{v + v_o}{v - v_s} ight) = 600 \left( \frac{330 + 30}{330 - 30} ight) = 600 \left( \frac{360}{300} ight) = 720 \ Hz$.

The driver of a car travelling with speed $30 \ m/s$ towards a hill sounds a horn of frequency $600 \ Hz$. If the velocity of sound in air is $330 \ m/s$,the frequency of the reflected sound as heard by the driver is .... $Hz$

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