JCECE Engineering JCECE Engineering Solved Paper-2005

  • question_answer
    An elastic ball is dropped from a height \[h\] and it rebounds many times from the floor. If the coefficient of restitution is \[e\], the time interval between the second and the third impact, is:

    A) \[\frac{ev}{g}\]                                

    B) \[\frac{{{e}^{2}}v}{g}\]

    C) \[{{e}^{2}}\sqrt{\left( \frac{8h}{g} \right)}\]                       

    D) \[{{e}^{2}}\sqrt{\left( \frac{h}{g} \right)}\]

    Correct Answer: C

    Solution :

    Key Idea: Assume initial velocity to be zero. From equation of motion\[h=ut+\frac{1}{2}g{{t}^{2}}\]when      \[u=0,\,\,t=\sqrt{\frac{2h}{g}}\] The second impact occurs after an additional time\[=2\sqrt{2{{h}_{1}}g}=2e\sqrt{2h/g}\]             \[(\because \,\,{{h}_{1}}={{e}^{2}}h)\] The third impact occurs after an additional time\[=2\sqrt{2{{h}_{2}}g}=2{{e}^{2}}\sqrt{2h/g}={{e}^{2}}\sqrt{8h/g}\] \[(\because \,\,{{h}_{2}}={{e}^{4}}h)\]


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