JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन Question Bank Pressure and Density

  • question_answer
    A body of density \[{{d}_{1}}\]is counterpoised by \[Mg\] of weights of density \[{{d}_{2}}\] in air of density d. Then the true mass of the body is

    A)            M  

    B)            \[M\,\left( 1-\frac{d}{{{d}_{2}}} \right)\]                    

    C)            \[M\left( 1-\frac{d}{{{d}_{1}}} \right)\]                        

    D)            \[\frac{M(1-d/{{d}_{2}})}{(1-d/{{d}_{1}})}\]

    Correct Answer: D

    Solution :

                       Let \[{{M}_{0}}=\]mass of body in vacuum. Apparent weight of the body in air = Apparent weight of standard weights in air \[\Rightarrow \] Actual weight ? upthrust due to displaced air       = Actual weight  ? upthrust due to displaced air            \[\Rightarrow \]\[{{M}_{0}}g-\left( \frac{{{M}_{0}}}{{{d}_{1}}} \right)\,dg=Mg-\left( \frac{M}{{{d}_{2}}} \right)\,dg\]                                     \[\Rightarrow {{M}_{0}}=\frac{M\left[ 1-\frac{d}{{{d}_{2}}} \right]}{\left[ 1-\frac{d}{{{d}_{1}}} \right]}\]


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