A bat moving at 10 ms -1 towards a wall sends a sound signal of 8000 Hz towards it. On reflection it hears a sound of frequency f. The value of f in Hz is close to

(speed of sound=320 ms-1)

  • Option 1)

    8258

  • Option 2)

    8516

  • Option 3)

    8000

  • Option 4)

     8424

     

 

Answers (1)

As we learnt in

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

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

- wherein

C= Speed of sound

V_{0}= Speed of observer

V_{\Delta }= speed of source

\nu _{0 }= Original frequency

\nu {}'= apparent frequency

 

 Reflected frequency of sound reaching bat.

\upsilon'=\left[\frac{v-(-v_{0})}{v-v_{s}} \right ]\upsilon=\left[\frac{v+v_{0}}{v-v_{s}} \right ]\upsilon=\frac{v+10}{v-10}\upsilon

=\left(\frac{320+10}{320-10} \right )\times=8516\ Hz

Correct option is 2.

 


Option 1)

8258

This is an incorrect option.

Option 2)

8516

This is the correct option.

Option 3)

8000

This is an incorrect option.

Option 4)

 8424

 

This is an incorrect option.

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