Question

8. A train moving at a speed of 220 ms towards a
stationary object, emits a sound of frequency 1000Hz
Some of the sound reaching the object gets reflected
back to the train as echo. The frequency of the echo as
detected by the driver of the train is:
(Speed of sound in air is 330 ms)
(A) 5000 Hz (B) 3000 Hz
(C) 3500 Hz (D) 4000 Hz

any genius is there
pls answer my question as fast as you can ​

Answer 1

Option B is correct !!

step are ...

look in this attachement !!

hope it help you ..

Where , u is speed of sound in medium

u0 = speed of observer with respect to medium

here the observer is in rest so u0 = 0 (zero )

Us = speed of source with respect to medium

f = frequency emitted by source

f '= new frequency.

Answer 2

↧↧↧↧↧↧↧↧↧↧↧↧↧↧↧↧

Frequency of sound reached at the stationary object:n'=[v+vo / v−vs]n=[330+0 / 330−220]×1000

=330/ 110×1000=3000

 HzFrequency of reflected sound:

n''=[v+vo/ v−vs]n'

=[330+220/ 330−0]×3000

=550 / 330×3000=5000

 

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