JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन JEE PYQ-Fluid Mechanics, Surface Tension and Viscosity

  • question_answer
    A wooden block floating in a bucket of water has\[\frac{4}{5}\]of its volume submerged. When certain amount of an oil is poured into the bucket, it is found that the block is just under the oil surface with half of its volume under water and half in oil. The density of oil relative to that of water is:                                         [JEE Main 9-4-2019 Afternoon]

    A)  0.5                  

    B)       0.7

    C)  0.6

    D)       0.8

    Correct Answer: C

    Solution :

    [c] In 1st situation
    \[{{V}_{b}}{{\rho }_{b}}g={{V}_{s}}{{\rho }_{w}}g\]
    \[\frac{{{V}_{s}}}{{{V}_{b}}}=\frac{{{\rho }_{b}}}{{{\rho }_{w}}}=\frac{4}{5}\]                              …(i)
    here \[{{V}_{b}}\] is volume of block
    \[{{V}_{s}}\] is submerged volume of block
    \[{{\rho }_{b}}\] is density of block
    \[{{\rho }_{w}}\] is density of water
    & Let \[{{\rho }_{o}}\] is density of oil
    finally in equilibrium condition
    \[{{V}_{b}}{{\rho }_{b}}g=\frac{{{V}_{b}}}{2}{{\rho }_{o}}g+\frac{{{V}_{b}}}{2}{{\rho }_{w}}g\]
    \[2{{\rho }_{b}}={{\rho }_{0}}+{{\rho }_{w}}\]
    \[\Rightarrow \]\[\frac{{{\rho }_{o}}}{{{\rho }_{w}}}=\frac{3}{5}=0.6\]             


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