A bus is moving with a velocity of `5 ms^(-1)` towards a huge wall. The driver sound a horn of frequency 165 Hz. If the speed of sound in air is `335 ms^(-1)`, the number of beats heard per second by a passenger inside the bus will be

Options

A. 3
B. 4
C. 5
D. 6

Answer

A

Explanation

The apparent frequency of sound striking the wall,
`v . = ( v xx v )/( ( v - v_s)) = (335 xx 165)/( (335- 5)) = (335)/(2)" Hz" = 167" Hz"`
For reflected sound, wall is the source and passenger in the bus is observer.
`therefore v.. = ((v + v_O) v.)/(v ) = ((335 + 5))/(335) xx (335)/(2) = 170" Hz"`
`therefore` Number of beats per second `= v.. - v = 170 - 167 = 3`