Q.

A source of sound with frequency  f0=1700Hz and an observer are at the same point.  At  t=0, the source starts receding from the observer with a constant acceleration a=10m/s2. The velocity of the sound in air is  V=340m/s. then chose the correct  option(s).
 

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a

The sound emitted by the source at  t=8.8sec (approximately) is received by the stationary observer at  t=10sec.

b

The frequency of sound received by the stationary observer at  t=10sec is  approximately 1550 HZ

c

The frequency of sound received by the stationary observer at  t=10sec is  approximately 1350 HZ

d

The sound emitted by the source at  t=6.8sec (approximately) is received by the stationary observer at  t=10sec.

answer is A, D.

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Detailed Solution

Let the sound emitted by the source at time ‘t’ is received by the stationary observer at t =10 sec.
Question Image
 d=12at2=12×10t2=5t2
Now, d= 340(10-t)
5t2=340(10t)       t2+68t680=0      t=68±(68)2+4×6802

t = 8.8 (approximately) 

Vs=at=10×8.8=88m/s     Hence,  f=[vv+v0]t0

f=(340340+88)1700=1350HZ   (Approximately)  

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