The driver of a bus, approaching a big wall, notices that the frequency of his bus’s horn changes from 420Hzto490Hz when he hears it after it gets reflected from the wall. Find the speed of the bus, if the speed of the sound is 330ms–1
A
91km h−1
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B
81km h−1
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C
61km h−1
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D
71km h−1
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Solution
The correct option is A91km h−1 From the Doppler's effect of sound, frequency appeared/heard at the wall is,
fw=330330−v.f.....(i)
Here, v→ speed of bus, f→ actual frequency of the source,
The frequency (f′) heard by the driver of the bus, after reflection from the wall is,