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CMC Medical CMC-Medical VELLORE Solved Paper-2010

  • question_answer
    A ball is projected upward from the top of tower with a velocity 50\[m{{s}^{-1}}\]making angle \[30{}^\circ \] with the horizontal. The height of tower is 70 m. After how many seconds from the instant of throwing will the ball reach the ground?

    A)  2 s                                         

    B)  5 s

    C)  7 s                                         

    D)  9 s

    E)  None of these

    Correct Answer: C

    Solution :

    The vertical component of velocity of projection\[~=-\,50\text{ sin}\,30{}^\circ \] \[=-25\text{ }m\text{/}s\] If \[t\] be the time taken to reach the ground \[\therefore \]  \[h=ut+\frac{1}{2}g{{t}^{2}}\] \[70=-\,25\,t+\frac{1}{2}\times 10\times {{t}^{2}}\] \[70=-\,25\,t+5\,{{t}^{2}}\] \[{{t}^{2}}-5t-14=0\] \[t=-\,2s\]and \[7\,s\] Since \[t=-\,2\,s\] is not valid so \[t=7\,s\]


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