a sound source emits frequency of `180 h_(Z)` when moving towards a rigid wall with speed `5 m//s` and an observer is moving away from with speed `5 m//s`. Both source and observer moves on a straight line which is perpendicular to the wall. The number of beatd per second heard by the observer will be [speed of sound = `335 m//s`]

Options

A. `5 beats//s`
B. `10 beats//s`
C. `6 beats//s`
D. `8 beats//s`

Answer

A

Explanation

There is not relative motion between `O` and `S`' .
`overset(O)underset(5 m//s)(larr)``S_(rarr)5 m//s` |`overset(S')underset(5 m//s)(larr)`

`f_(b) = f_(S') - f_(S)`
= `f - f_(s) = 180 - 18-0 ((355 - 5) / (355 + 5))`
= `5 H_(Z)`