As shown if Fig. a vibrating tuning fork of frequency 512 Hz is moving towards the wall with a speed `2(m)/(s)`. Take speed of sound as `v=340(m)/(s)` and answer the following questions.
Q. If the listener is at rest and located such that the tuning fork is moving between the listener and the wall, number of beats heard by the listerner per second will be nearly

Options

A. 0
B. 6
C. 8
D. 4

Answer

D

Explanation

As the source is moving away from the listetner hence frequency observed by listerner is
`f_1=(v)/(v+v_S)f=(340)/(340+2)xx512`
`=(340)/(342)xx512=509Hz`
The frequency reflected from wall (we can assume an observer at rest) is
`f_2=(v)/(v-v_S)xxf`
`=(340)/(338)xx512=515Hz`
Therefore beats heard by observer `(L)` is `515-509=6`.