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  • Give answer! Two factories are sounding their sirens at 800 Hz. A man goes from one factory to other at a speed of 2 m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in one second will be :

Two factories are sounding their sirens  at 800 Hz.  A man goes from one  factory to other at a speed of 2 m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in one second will be :

  • Option 1)

    2

  • Option 2)

    4

  • Option 3)

    8

  • Option 4)

    10

 

Answers (1)

best_answer

As we learned

 

Beat Frequency -

\Delta \nu = \left | \nu _{1}-\nu _{2} \right |

module of \left ( \nu _{1} -\nu _{2}\right )

 

- wherein

Where \nu _{1} \: and\: \nu _{2} are frequency of two wave differ slightly  in value of frequency.

 

 

Frequency of sound when source and observer are moving towards each other -

\nu {}'= \nu _{0}.\frac{C+V_{0}}{C-V_{s}}
 

- wherein

C= Speed of sound

V_{0}= Speed of observer

V_{s}= speed of source

\nu _{0 }= Original frequency

\nu {}'= apparent frequency

 

 \upsilon _{1}=\upsilon _{0}\cdot \left ( \frac{c+v}{c} \right )=800\times \left ( \frac{322}{300} \right )

\upsilon _{2}=\upsilon _{0}\cdot \left ( \frac{c-v}{c} \right )=800\times \left ( \frac{320-2}{320} \right )

=800\times \left ( \frac{318}{320} \right )

\Delta \upsilon =800\left ( \frac{4}{320} \right )=10Hz

 

 

 


Option 1)

2

Option 2)

4

Option 3)

8

Option 4)

10

Posted by

prateek

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