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  • Two whistles A and B have frequencies 600 Hz and 590 Hz, respectively. An observer is standing in the middle of line joining the two sources.sources B and observer are moving towards right with vel

Two whistles A and B have frequencies 600 Hz and 590 Hz, respectively. An observer is standing in the middle of line joining the two sources.sources B and observer are moving towards right with velocity 30 m/s and A is standing to the left side.If the velocity of sound in air is 300 m/s.The number of beats per second listened by the observer are.

Option: 1

8 Hz


Option: 2

6 Hz


Option: 3

4 Hz


Option: 4

2 Hz


Answers (1)

best_answer

There is no relative motion between O and B , hence-

 

\mathrm{ f_B^{\prime}=f_B=590 \mathrm{~Hz} }

But

,\mathrm{ \begin{aligned} & f_A^{\prime}=f_B=590 \mathrm{~Hz} . \\ & f_A^{\prime}=f_A\left(\frac{V-v_0}{v}\right) \\ & f_A^{\prime}=660\left(\frac{300-30}{300}\right) \\ & f_A^{\prime}=594 \mathrm{~Hz} . \end{aligned} }

Beat frequency \mathrm{f_B=f_A^{\prime}-f_B^{\prime}=4 \mathrm{~Hz}}

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Shailly goel

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