JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2011

  • question_answer
        A rock is dropped from a 100 m high cliff. How long does it take to fall first 50 m and the second 50m?

    A)  \[2s,3s\]                             

    B)  \[1.5s,\text{ }2.5s\]

    C)  \[1.2s,\text{ }3.2s\]                       

    D)  \[3.2s,1.3s\]

    Correct Answer: D

    Solution :

                    Take the y-axis to be upward, at\[{{v}_{0}}=0\] and solve\[y={{v}_{0}}t-\frac{1}{2}g{{t}^{2}}\]for t \[\therefore \]  \[t=\sqrt{-2y/g}\] Here for \[y=-50\text{ }m\] So,          \[t=\sqrt{-\frac{2(50)}{9.8}}=3.2s\] Here,     \[y=-100m\]                 \[t=\sqrt{-\frac{2(-100)}{9.8}}=4.5\,s\] Hence, the difference is the time taken to fall the second 50 m. \[=4.5-3.2=1.3s\]


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