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  • Confused! kindly explain, A car sounding a horn of frequency 1000 Hz passes an observer. The ratio of frequencies of the horn noted by the observer before & after passing of the car is 11:9, If the speed of sound is v, the speed of car is

A car sounding a horn of frequency 1000 Hz passes an observer. The ratio of frequencies of the horn noted by the observer before & after passing of the car is 11:9, If the speed of sound is v, the speed of car is 

  • Option 1)

    \frac{1}{10} v

  • Option 2)

    \frac{1}{2} v

  • Option 3)

    \frac{1}{5} v

  • Option 4)

    v

 

Answers (1)

best_answer

n_{before}= \left ( \frac{v}{v-v_{s}} \right )n ,

n_{after}= \left ( \frac{v}{v+v_{s}} \right )n ,

\frac{n_{before}}{n_{after}}= \frac{11}{9}= \frac{v+v_{c}}{v-v_{c}}\Rightarrow v_{c}=\frac{v}{10}

 

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

 

 


Option 1)

\frac{1}{10} v

This is correct

Option 2)

\frac{1}{2} v

This is incorrect

Option 3)

\frac{1}{5} v

This is incorrect

Option 4)

v

This is incorrect

Posted by

prateek

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