Question

A source of sound and detector are moving as shown in Fig. at `t=0`. Take velocity of sound wave to be `v`. For this situation mark out the correct statement(s).
A. The frequency received by the detector is always greater than `f_0`
B. Initially, frequency received by the detector is greater than `f_0`, becomes equal to `f_0`, and then decreases with the time.
C. Frequency received by the detector is equal to `f_0` at `t=(dcottheta_0)/((2v_0))`.
D. Frequency received by the detector can never be equal to `f_0`

Answer 1

Correct Answer - B::C
As time increases, the source and detector are relatively approaching each other up to `t=t_0` where `t_0` is the instant when the source and detector are located perpendicular to direction of motion.
`v_0xxt_0=(dcottheta_0)/(2)`
`t_0=(dcottheta_0)/(2v_0)`
For `tltt_0`
`f_(ap)gtf_0`
For `tgtf_0`,
`f_(ap)ltf_0`