1.

A train moving towards a hill at a spped 72 km/her sounds a whistle of frequency 500 Hz. A wind is blowing from the hill at a speed of 36 km/hr. If the speed of sound in air is 340 m/s, the frequency heard by a man on the hill is

Answer»

532.5 Hz
565.0 Hz
516.0 Hz
None of the these .

SOLUTION :If f. represents the apparent frequency and f is the actual frequency then f. = `((V pm W)/((V pm w ) - U_(s))) ` f where V is the of VELOCITY of SOUND , w is velocity of wind and `U_(s)` is source .
Here observer is at rest
` therefore"" f. = ((340 - 10)/(340 -10 - 20)) 500 = 532.3 ` Hz
so correct choice is (a).


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