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

  • question_answer
    From the top of a building of height\[40\,\,m\], a boy throws a stone vertically upwards with an initial velocity of \[10\,\,m\,\,{{s}^{-1}}\] such that it eventually falls to the ground. At what time will the stone reach the ground?\[(g=10\,\,m{{s}^{-2}})\]

    A) \[4s\]                  

    B)        \[3s\]

    C) \[2s\]                            

    D) \[1s\]

    Correct Answer: A

    Solution :

    \[h=-ut+\frac{1}{2}g{{t}^{2}}\]\[40=-10t+\frac{1}{2}\times 10\times {{t}^{2}}\Rightarrow t=4\,\,s\]


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