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

Frequency heard by observer directly coming from source `=(355-5)/(355+5) times 180=175 Hz`
`f_2 to` frequency heard by observer after reflection
`[355/(355-5)times][(355-5)/355]times180=180Hz`
`f_2-f_1=5Hz`