JEE Main & Advanced Physics Rotational Motion Question Bank Mock Test - Centre of Mass, Conservation of Linear Momentum and Collisions

  • question_answer
    Two particles \[A\] and \[B\] start moving due to their mutual interaction only. If at any time\[t\], \[{{\vec{a}}_{A}}and\,{{\vec{a}}_{B}}\] are their respective accelerations, \[{{\vec{v}}_{A}}\,and\,{{\vec{v}}_{B}}\] are their respective velocities, and up to that time \[{{W}_{A\,}}and\,{{W}_{B}}\] are the work done on \[A\] and \[B\] respectively by the mutual force, \[{{m}_{A\,}}and\,{{m}_{B}}\] are their masses respectively, then which of the following is always correct?

    A) \[{{\vec{v}}_{A}}\,+\,{{\vec{v}}_{B}}=0\]    

    B) \[{{m}_{A\,}}{{\vec{v}}_{A}}+\,{{m}_{B}}{{\vec{v}}_{B}}=0\]

    C) \[{{W}_{A}}\,+\,{{W}_{B}}=0\]        

    D) \[{{\vec{a}}_{A}}+{{\vec{a}}_{B}}=0\]

    Correct Answer: B

    Solution :

    [b] Since \[\Sigma {{\vec{F}}_{ext}}=\vec{0}\Rightarrow {{m}_{A}}{{\vec{a}}_{A}}+{{m}_{B}}{{\vec{a}}_{B}}=0\]   \[\therefore \]Momentum of system will remain conserved, equal to zero. \[{{m}_{A}}{{\vec{v}}_{A}}+{{m}_{B}}{{\vec{v}}_{B}}=0\] But \[{{W}_{A}}+{{W}_{B}}\ne 0\]


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