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9th Class Science Gravitation and Floatation Question Bank Gravitation and Pressure

  • question_answer
    A stone is dropped from a tower. It was found that it covered a distance of \[45\,\,m\] during its last second of the fall. Calculate the time of the fall and the height of the tower?\[(g=10\,\,m\,\,{{s}^{-2}})\]

    A) \[5s,\,\,45m\]     

    B)        \[10s,\,\,90m\]

    C) \[5s,\,\,125m\]     

    D)        \[10s,\,\,100m\]

    Correct Answer: C

    Solution :

     During the last second it fell through\[45\,\,m\] \[{{S}_{n}}=\frac{g}{2}(2n-1),\,\,45=\frac{10}{2}(2n-1)\Rightarrow n=5\,\,s\] Time of flight is\[5\,\,s\]. Therefore, the height of the tower:             \[S=\frac{1}{2}\times g\times {{t}^{2}}=\frac{1}{2}\times 10\times 25=125\,\,m\]


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