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

  • question_answer
    The total mass of an elevator, with a 80 kg man in it, is 1000 kg. This elevator moving upward with a speed of 8 m/s is brought to rest over a distance 16 m. Then tension T in the cable supporting elevator is

    A)  3200 N          

    B)         5400 N

    C)  6500 N          

    D)         7800 N  

    Correct Answer: D

    Solution :

     Acceleration a of the elevator is given by             \[{{v}^{2}}-{{u}^{2}}=2as\] \[\Rightarrow \]   \[0-64=2\times a\times 16\] \[\Rightarrow \]   \[a=-2\,\,m/{{s}^{2}}\] Let \[M\] be the total mass of the elevator, then             \[T-Mg=Ma\] \[\Rightarrow \]   \[T=M(g+a)\]             \[=1000(9.8+2)\]             \[=\mathbf{7800}\,\,\mathbf{N}\].


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