Discussion Forum : Sound
Question -
Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/h and 36 km/h. If second car blows horn of frequency 280 Hz, then the frequency of horn heard by the driver of first car when the line joining the cars makes angle of 45∘ with the roads, will be (velocity of sound is 330 m/s)
Answer: Option B
:
B
The component of velocity of source along line joining the car is
vs=v1 cos 45∘=36×1√2 km/h
=5√2 m/s
Component of velocity of observer(second car) along the line joining the car is
V0=v2 cos 45∘=72×1√2 km/h
=10√2 m/s
n′=v+v0v−vs n=330+10√2330−5√2×280
=344323×280 Hz=298 Hz
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:
B
The component of velocity of source along line joining the car is
vs=v1 cos 45∘=36×1√2 km/h
=5√2 m/s
Component of velocity of observer(second car) along the line joining the car is
V0=v2 cos 45∘=72×1√2 km/h
=10√2 m/s
n′=v+v0v−vs n=330+10√2330−5√2×280
=344323×280 Hz=298 Hz
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