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Railways NTPC (Technical Ability) Engineering Mechanics and Strength of Materials Question Bank Engineering Mechanics

  • question_answer
    A cord is used to lower vertically a block of mass M a distance d at a constant downward acceleration of g/4. Then the work done by the cord on the block is:

    A) \[Mgd/4\]                      

    B) \[3\,Mgd/4\]

    C) \[-\,3\,Mgd/4\]                

    D) \[Mgd\]

    Correct Answer: C

    Solution :

    \[T\text{ }=\text{ }Mg,\text{ }F=Ma\text{ }=\text{ }Mg/4\] Net force \[=\,\,\text{Mg/4}-Mg=-\,\text{3}\,\,\text{Mg/4}\] Work done \[=-\text{3}\,\,\text{Mg}\,\text{d/4}\]


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