Sound WavesHardBloom L3

Question

A train moving towards a hill at a speed of 72 km / hr 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.516.1 Hz.
D.none of the above.

Solution

Sol. vt = 72 km/hr = 20 m/s

vw = 36 km/hr = 10 m/s

f = $\left( \frac{v_{sound} - v_{man/wind}}{v_{sound} - v_{t/wind}} \right) \times 500$

= $\left( \frac{340 - 10}{340 - 30} \right)500$ = 532 Hz

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