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9th Class Science Sound Question Bank Sound Formative Objective Problems

  • question_answer
    A man standing near a cliff with a seconds pendulum fires a gun when the pendulum is at the mean position and hears the echo when it just reaches the extreme position. If the speed of sound is\[\text{34}0\,\text{m}{{\text{s}}^{-\text{1}}}\], calculate his distance from the cliff.

    A)  80 m                                    

    B)  85 m

    C)  75 m                                    

    D)  70 m

    Correct Answer: B

    Solution :

      Let the distance be ?d?. The time taken for one complete oscillation (i.e., the time period) by a seconds pendulum = 2s \[\therefore \]The time taken for it to move from the mean to the extreme position\[=\frac{1}{4}\times 2s=0.5s\] \[\therefore \]speed of sound\[=340\text{ }m{{s}^{1}}.\] Distance travelled by sound before the echo is heard = 2d \[2d=speed\times time\] \[2d=340\times 0.5\]\[\Rightarrow \]\[d=85\text{ }m\]


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