JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन Question Bank Self Evaluation Test - Mechanical Properties of Fluids

  • question_answer
    In the arrangement as shown,\[{{m}_{B}}=3m\], density of liquid is r and density of block B is v. The system is released from rest so that block B moves up when in liquid and moves down when out of liquid with the same acceleration. Find the mass of block A.    

    A) \[\frac{7}{4}m\]

    B) \[2m\]

    C) \[\frac{9}{2}m\]

    D) \[\frac{9}{4}m\]

    Correct Answer: D

    Solution :

    [d] Acceleration when block B is in the liquid \[{{a}_{1}}=\frac{{{m}_{A}}g-({{m}_{B}}g-upthrust)}{({{m}_{A}}+3m)}\] \[=\frac{{{m}_{A}}g-\left( 3mg-\frac{3m}{2\rho }\rho g \right)}{({{m}_{A}}+3m)}\uparrow \] Acceleration when block B is outside if the liquid,   \[{{a}_{2}}=\frac{3mg-{{m}_{A}}g}{({{m}_{A}}+3m)}(\downarrow )\] \[Given\,{{a}_{1}}={{a}_{2}}\], we get \[{{m}_{A}}g-\frac{3}{2}mg=3mg-{{m}_{A}}g\] \[\Rightarrow \,\,\,2{{m}_{A}}g-\frac{9}{2}mg\Rightarrow {{m}_{A}}=\left( \frac{9}{4} \right)m\]


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