JEE Main & Advanced Physics Motion in a Straight Line / सरल रेखा में गति Question Bank Critical Thinking Questions

  • question_answer
    A particle is dropped vertically from rest from a height. The time taken by it to fall through successive distances of 1 m each will then be           [Kurukshetra CEE 1996]

    A)             All equal, being equal to \[\sqrt{2/g}\] second

    B)             In the ratio of the square roots of the integers 1, 2, 3.....

    C) (c) In the ratio of the difference in the square roots of the integers i.e. \[\sqrt{1},\,(\sqrt{2}-\sqrt{1}),\,(\sqrt{3}-\sqrt{2}),\,(\sqrt{4}-\sqrt{3})\]...

    D)             In the ratio of the reciprocal of the square roots of the integers i.e.,.  \[\frac{1}{\sqrt{1}},\,\frac{1}{\sqrt{2}},\frac{1}{\sqrt{3}},\,\frac{1}{\sqrt{4}}\]

    Correct Answer: C

    Solution :

                    \[h=ut+\frac{1}{2}g{{t}^{2}}\Rightarrow 1=0\times {{t}_{1}}+\frac{1}{2}gt_{1}^{2}\Rightarrow {{t}_{1}}=\sqrt{2/g}\] Velocity after travelling 1m distance \[{{v}^{2}}={{u}^{2}}+2gh\Rightarrow {{v}^{2}}={{(0)}^{2}}+2g\times 1\Rightarrow v=\sqrt{2g}\] For second 1 meter distance \[1=\sqrt{2g}\times {{t}_{2}}+\frac{1}{2}gt_{2}^{2}\Rightarrow gt_{2}^{2}+2\sqrt{2g}{{t}_{2}}-2=0\] \[{{t}_{2}}=\frac{-2\sqrt{2g}\pm \sqrt{8g+8g}}{2g}=\frac{-\sqrt{2}\pm 2}{\sqrt{g}}\] Taking +ve sign \[{{t}_{2}}=(2-\sqrt{2})/\sqrt{g}\]                         \[\therefore \]\[\frac{{{t}_{1}}}{{{t}_{2}}}=\frac{\sqrt{2/g}}{(2-\sqrt{2})/\sqrt{g}}=\frac{1}{\sqrt{2}-1}\] and so on.


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