A sound source of frequency f₀=130 ~Hz is dropped from a height slightly greater than 250 m above the ground. At the same time a detector is thrown upwards with velocity u =50 ~ms ⁻¹ along the same line. If the speed of sound is v=300 ~ms ⁻

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A sound source of frequency f₀=130 ~Hz is dropped from a height slightly greater than 250 m above the ground. At the same time a detector is thrown upwards with velocity u =50 ~ms ⁻¹ along the same line. If the speed of sound is v=300 ~ms ⁻¹ , if the frequency (in Hz ) detected by the detector after t =5 ~s is 39 n , find the value of n ( . Take . g =10 ~ms ⁻² )

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Correct answer: 4

After 5 s , speed of detector =50-10 5=0 and that of source =0+10 5=50 ~m / s and the source has fallen a distance = 1 2 10 (5)^2=125 ~m and the detector has rises a distance =50 5- 1 2 10(5)^2=125 ~m So, f^ =130 ( 300-0 300-50 )=156 ~Hz .

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