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BCECE Engineering BCECE Engineering Solved Paper-2009

  • question_answer
    23.      From the top of a building 40 m tall, a boy projects a Stone vertically upwards with an initial velocity \[10\,m{{s}^{-1}}\] such that it eventually falls to the ground. After how long will the stone strike the ground? Take \[g=10\,m{{s}^{-2}}\]

    A)  1 s                                         

    B)  2 s

    C)  3 s                         

    D)         4 s

    Correct Answer: D

    Solution :

     \[S=ut+\frac{1}{2}g{{t}^{2}}\] or            \[40=-10\,t+\frac{10}{2}{{t}^{2}}\] or            \[{{t}^{2}}-2t-8=0\] or            \[(t+2)(t-4)=0\] \[\Rightarrow \,\,t=4\,s\] t cant be negative.


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