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9th Class Science Force and laws of motion Question Bank Force and Laws of Motion

  • question_answer
    A lift is moving down with a retardation of\[5\,\,m\,\,{{s}^{-2}}\]. Calculate the percentage change in the weight of the person in the lift\[(g=10\,\,m\,\,{{s}^{-2}})\].

    A) \[-25\]                           

    B) \[-50\]  

    C) \[-75\]                           

    D) \[-100\]

    Correct Answer: B

    Solution :

     \[W=mg=10\,\,m\,\,N\] When lift is moving downwards, the apparent weight is given as: \[W=m(g-a)=m(10-5)=5\,\,m\,\,N\]\[%\]Change in weight\[=\frac{{{w}_{1}}-w}{w}\times 100=\frac{5\,\,m-10\,\,m}{10\,\,m}\times 100\] \[=-\frac{1}{2}\times 100=-50%\]


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