JEE Main & Advanced Physics NLM, Friction, Circular Motion Question Bank Topic Test - Newton's Laws Of Motion

  • question_answer
    In the system shown in figure \[{{m}_{A}}=4m,\,\,{{m}_{B}}=3m\] and \[{{m}_{C}}=8m\]. Friction is absent everywhere. String is light and inextensible. If the system is released from rest find the acceleration of block B

    A) \[\frac{g}{8}\]

    B) \[\frac{g}{2}\]

    C) \[\frac{g}{4}\]

    D) g

    Correct Answer: B

    Solution :

    [b]
    \[a=b+c\] [string constrained]
    \[T={{m}_{B}}b\] [Newton's II law for B in horizontal direction]
    \[T=[{{m}_{A}}+{{m}_{C}}]c\] [Newton's I law for A and C in horizontal direction]
    \[{{m}_{A}}g-T={{m}_{A}}a\] [Newton's I law for A and C in horizontal direction]
    \[\frac{{{m}_{A}}g-T}{{{m}_{A}}}=\frac{T}{{{m}_{B}}}+\frac{T}{{{m}_{A}}+{{m}_{C}}}\]
    \[\frac{4mg-T}{4m}=\frac{T}{3m}+\frac{T}{12m}\]
    \[\Rightarrow \]   \[T=\frac{3mg}{2}\Rightarrow b=\frac{g}{2}\]
     


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