question_answer

A source of sound A emitting waves of frequency 1800 Hz is falling towards ground with a terminal speed v. The observer B on the ground directly beneath the source receives waves of frequency 2150 Hz. The source A receives waves, reflected from ground of frequency nearly: (Speed of sound  = 343 m/s)                             [JEE ONLINE 12-04-2014]

A)  2150 Hz          

B)       2500 Hz

C)  1800 Hz          

D)       2400 Hz

Correct Answer: B

Solution :

[b] Given

Reflected wave frequency received by A,

Applying doppler’s effect of sound, here,

Now, for the reflected wave,