Waves - Result Question 70

72. A source of sound S emitting waves of frequency 100Hz and an observor O are located at some distance from each other. The source is moving with a speed of 19.4ms1 at an angle of 60 with the source observer line as shown in the figure. The observor is at rest. The apparent frequency observed by the observer is (velocity of sound in air 330ms1 )

[2015 RS]

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Answer:

Correct Answer: 72. (a)

Solution:

  1. (a) Here, original frequency of sound, f0=100 Hz

Speed of source Vs=19.4cos60=9.7

19.4cos60=9.7

From Doppler’s formula

f=f0(VV0VVs)

f=100(V0V(+9.7))

f=100VV(19.7V)=100(19.7330)

=103Hz

Apparent frequency ff=103Hz



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