Two factories are sounding their sirens at 800 Hz. A man goes from one factory t

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Two factories are sounding their sirens at 800 Hz. A man goes from one factory to the other at a speed of 2 m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in 1 s will be

Options:

A . 2

B . 4

C . 8

D . 10

Answer: Option D
:
D
When the man is approaching the factory,

n^{'} = (\frac{v + v_{0}}{v}) n = (\frac{320 + 2}{320}) 800 = (\frac{322}{320}) 800

When the man is going away from the factory,

n "= (\frac{v - v_{0}}{v}) n = (\frac{320 - 2}{320}) 800 = (\frac{318}{320}) 800 ∴ n^{'} - n "= (\frac{320 - 318}{320}) 800 = 10 H z

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