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JEE Main & Advanced Physics Question Bank Oblique Projectile Motion

  • question_answer
    A ball is projected upwards from the top of tower with a velocity \[50\,\,m{{s}^{-1}}\] making an angle \[{{30}^{o}}\] 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                                     [DPMT 2004]

    A)             2 s       

    B)           5 s

    C)             7 s       

    D)             9 s

    Correct Answer: C

    Solution :

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


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