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

Options

A. 620Hz
B. 680Hz
C. 720Hz
D. 840Hz

Answer

B

Explanation

Effective value of velocity of source is
`V_(S)=(100)/(3)costheta`
`=(100)/(3)xx(3)/(5)=20m//s`
`V'=(V)/(V-V_(S))V`
`V'=(340)/(340-20)xx640Hz=680Hz`