JEE Main & Advanced Sample Paper JEE Main - Mock Test - 6

  • question_answer
    A cubical block is placed on a thin liquid layer of thickness\[0.2\text{ }mm\]. The load moves downward with a constant speed of \[2\text{ }cm/sec\]after the system is released. If coefficient of viscosity of liquid is \[\frac{x}{1000}Pa-\sec ,\] then x is (Take\[g=10m/{{s}^{2}}\])               '

    A) 3                       

    B) 5                

    C) 7                       

    D) 9                                 

    Correct Answer: B

    Solution :

       [b] By constraint relation, velocity of block is 2K As acceleration for block and disc is zero, for disc \[2T=mg\] \[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,T=\frac{mg}{2}\] and for block \[T=f\] \[\Rightarrow \,\,\,\,\,\frac{mg}{2}=\eta A\frac{2V}{d}\Rightarrow \eta =\frac{mgd}{4AV}\] \[=\frac{20\times {{10}^{-3}}\times 10\times 0.2\times {{10}^{-3}}}{4\times {{10}^{3}}\times {{10}^{-4}}\times 2\times {{10}^{-2}}}=5\times {{10}^{-3}}NS{{m}^{-2}}\]   

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