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

Options

A. 532.5 Hz
B. 565.0 Hz
C. 516.0 Hz
D. None of the these .

Answer

A

Explanation

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).