9th Class Science Sound-152 Question Bank Sound

  • question_answer A man standing in front of a large wall claps at a regular frequency of 10 Hz. He finds that the echoes coincide with his clapping. (The speed of sound in air is \[330\text{ }m\text{ }{{s}^{-1}}\].)
    (i)  Time taken between successive clapping is 0.1 s.
    (ii) The distance between the man and the wall, after he stops clapping, if he hears one more echo is 33 m.
    (iii) The distance between the man and the wall, after he stops clapping, if he hears four more echoes is 66 m.

    A) Only (i) and (ii) are correct.

    B) Only (ii) and (iii) are correct.

    C) Only (i) and (iii) are correct.

    D) All (i), (ii) and (iii) are correct.

    Correct Answer: C

    Solution :

    (i) Time taken between successive clapping\[=\frac{1}{10}s=0.1s\] (ii) Since one echo is heard, so the time taken between the last clap and its echo \[=\frac{1}{10}s\] Distance \[=330\times \frac{1}{10}\times \frac{1}{2}=16.5m\] (iii) Since four echoes are heard, the time taken between the last clap and the echo \[=4\times \frac{1}{10}=\frac{4}{10}s\] Distance \[=330\times \frac{1}{10}\times \frac{1}{2}=16.5m\]

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