JEE Main & Advanced Sample Paper JEE Main Sample Paper-32

  • question_answer
    Four particles A, B, C and D of equal masses are placed at the comers of a square. They move with equal uniform speed V towards the intersection of the diagonals. After collision A comes to rest, B traces its path back with same speed and C and D move with equal velocities. What is the velocity of C after collision.

    A) \[\frac{2V}{3}\]       

    B)                                    \[2V\]

    C) \[\frac{V}{2}\]         

    D)                                    \[V\]

    Correct Answer: C

    Solution :

    \[{{F}_{ext}}=0,\]since \[{{a}_{CM}}=0\]                 \[\vec{p}={{\rho }_{A}}+{{\rho }_{B}}+{{\rho }_{C}}+{{\rho }_{D}}=\]constant If we resolve \[{{\rho }_{A}},{{\rho }_{B}},{{\rho }_{C}}\]  and \[{{\rho }_{D}}\] In horizontal and vertical directions, we find that initially \[\vec{p}={{\rho }_{A}}+{{\rho }_{B}}+{{\rho }_{C}}+{{\rho }_{D}}=0\] So, finally \[{{\rho }_{A}}+{{\rho }_{B}}+{{\rho }_{C}}+{{\rho }_{D}}=0\] \[{{\rho }_{A}}=0,\] \[{{\rho }_{B}}=-{{\rho }_{B}}\] \[{{\rho }_{C}}={{\rho }_{D}}\] or            \[2{{\rho }_{C}}={{\rho }_{B}}\]                 \[2m{{V}_{C}}=m{{V}_{B}}=mv\]                 \[{{V}_{C}}=\frac{V}{2}\]


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