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NEET Sample Paper NEET Sample Test Paper-8

  • question_answer
    An isolated particle of mass m is moving in horizontal plane (X-Y), along the X-axis, at a certain height above ground. It suddenly explodes into two fragments of masses m/4 and 3m/4). An instant later, the smaller fragment is at \[Y=+15\,cm.\]. The larger fragment at this instant is at:

    A)  \[Y=-5cm\]  

    B)  \[Y=+20cm\]

    C)  \[Y=+5cm\]         

    D)  \[Y=-20cm\]

    Correct Answer: A

    Solution :

    Before explosion, particle was moving along X-axis, i.e. It has no Y-component of velocity therefore, the centre of mass will not move in Y-direction or we can say \[Ycm=0\]. (Here note the wind explosion in due to only the internal forces) Now,          \[Ycm=\frac{{{m}_{1}}{{Y}_{1}}+{{m}_{2}}{{Y}_{2}}}{{{m}_{1}}+{{m}_{2}}}\] Therefore,         \[0-\frac{\left( \frac{m}{4} \right)(15)+\left( \frac{3m}{4} \right)(Y)}{\left( \frac{m}{4}+\frac{3m}{4} \right)}\] or               \[Y=-5cm\] (negative sign shows the downward distance) Similarly the change in X-coordinate of the centre of mass will also be zero.


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