JEE Main & Advanced JEE Main Paper (Held On 26 May 2012)

  • question_answer
    A point particle is held on the axis of a ring of mass m and radius r at a distance r from its centre C. When released, it reaches C under the gravitational attraction of the ring. Its speed at C will be.   JEE Main Online Paper (Held On 26-May-2012)  

    A) \[\sqrt{\frac{2Gm}{r}\left( \sqrt{2}-1 \right)}\] 

    B)                        \[\sqrt{\frac{Gm}{r}}\]

    C)                        \[\sqrt{\frac{2Gm}{r}\left( 1-\frac{1}{\sqrt{2}} \right)}\]

    D)                        \[\sqrt{\frac{2Gm}{r}}\]

    Correct Answer: C

    Solution :

                    Let 'M' be the mass of the particle Now,\[{{E}_{initial}}={{E}_{final}}\] i.e.\[\frac{GMm}{\sqrt{2}r}+0=\frac{GMm}{r}+\frac{1}{2}M{{V}^{2}}\]or\[\frac{1}{2}M{{V}^{2}}=\frac{GMm}{r}\left[ 1-\frac{1}{\sqrt{2}} \right]\] \[\Rightarrow \]\[\frac{1}{2}{{V}^{2}}=\frac{Gm}{r}\left[ 1-\frac{1}{\sqrt{2}} \right]\] or\[V=\sqrt{\frac{2Gm}{r}\left[ 1-\frac{1}{\sqrt{2}} \right]}\]


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