Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/hr and 36 km/hr. If first car blows horn of frequency 280 Hz, then the frequency of horn heard by the driver of second car when line joining the cars make 45° angle with the roads; will be

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321 Hz

298 Hz

289 Hz

280 Hz

answer is B.

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Detailed Solution

Here vA=72 km/hr=20m/secvB=36km/hr=10m/secn'=nv+vBcos45ov−vAcos45o⇒n'=280 340+10/2340−20/2=298 Hz

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