JEE Main & Advanced Sample Paper JEE Main Sample Paper-23

  • question_answer
    A body is projected vertically upwards. The times corresponding to height h while ascending and while descending are \[{{t}_{1}}\] and \[{{t}_{2}}\] respectively. Then, the velocity of projection is (g is acceleration due to a, gravity)

    A)  \[g\sqrt{{{t}_{1}}{{t}_{2}}}\]                         

    B)  \[\frac{g{{t}_{1}}{{t}_{2}}}{{{t}_{1}}+{{t}_{2}}}\]

    C)  \[\frac{g\sqrt{{{t}_{1}}{{t}_{2}}}}{2}\]                      

    D)  \[\frac{g({{t}_{1}}+{{t}_{2}})}{2}\]

    Correct Answer: D

    Solution :

    In case of motion under gravity, time taken to go up is equal to the time taken to fall down through the same distance. As, time of descent \[({{t}_{2}})=\] time of ascent \[({{t}_{1}})=\frac{2u}{g}\] \[\therefore \] Total time of flight \[T={{t}_{1\,}}+{{t}_{2}}\,=\frac{2u}{g}\]or \[u=\frac{g({{t}_{1}}+{{t}_{2}})}{2}\]


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