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

  • question_answer
    Three blocks are initially placed as shown in the figure. Block \[A\] has mass m and initial velocity \[v\] to the right. Block \[B\] with mass and block C with mass \[4m\] are both initially at rest. Neglect friction. All collisions are elastic. The final velocity of blocks \[A\] is

    A) 0.6\[v\]to the left

    B) 1.4\[v\]to the left

    C) \[v\] to the left  

    D) 0.4 \[v\] to the right

    Correct Answer: A

    Solution :

    [a]  Since, A and 5 have same mass. So, after elastic collision, they interchange their velocity. \[\therefore {{v}_{B}}=v\] After collision between B and C, \[v{{'}_{B}}=\left( \frac{m-4m}{m+4m} \right)v+\left( \frac{2\times 4m\times 0}{m+4m} \right)=-\frac{3}{5}v\] Again, collision takes place between A and B. So, velocity will be interchanged. \[\therefore v{{'}_{A}}=(v{{'}_{B}})=\frac{3}{5}v\] toward left


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