9th Class Science Sound Question Bank Sound

  • question_answer
    If the pitch of the sound of a source appears to drop by 10% to a moving person, then the velocity of motion is (velocity of sound = 330 m/sec)

    A)  33 m/sec              

    B)                    47 m/sec            

    C)                    56 m/sec                               

    D)  63 m/sec                               

    Correct Answer: A

    Solution :

                    \[n'=n\left( \frac{v-{{v}_{0}}}{v-{{v}_{s}}} \right)\] Given:   \[\frac{n'}{n}=\frac{90}{100}\]                 \[v=330\,\,m/s\] and\[{{v}_{s}}=0\] \[\therefore \]  \[\frac{90}{100}=\frac{330-{{v}_{0}}}{330-0}\] \[\Rightarrow \]               \[330-{{v}_{0}}=\frac{99}{100}\times 330=297\] \[\Rightarrow \]                         \[{{v}_{0}}=330-297=33\,\,m/\sec \]


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