A source of sound S is travelling at 1003 m/s along a road, towards a point A.

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A source of sound S is travelling at $\frac{100}{3} m / s$ along a road, towards a point A. When the source is 3 m away from A, a person standing at a point O on a road perpendicular to AS hears a sound of frequency v’. The distance of O from A at that time is 4m. If the original frequency is 640 Hz, then the value of v’ is (velocity of sound is 340 m/s)

Options:

A . 620 Hz

B . 680 Hz

C . 720 Hz

D . 840 Hz

Answer: Option B
:
B
Effective value of velocity of source is

A Source Of Sound S Is Travelling At 1003 m/s Along A Road,...

v_{s} = \frac{100}{3} c o s θ

= \frac{100}{3} \times \frac{3}{5} = 20 m / s

v^{'} = \frac{v}{v - v_{s}} v

v^{'} = \frac{340}{340 - 20} \times 640 H z = 680 H z

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