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

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    Two bodies are in equilibrium when suspended in water from the arms of a balance. The mass of one body is 36 g and its density is 9 g / cm3. If the mass of the other is 48 g, its density in g / cm3 is [CBSE PMT 1994]

    A)            \[\frac{4}{3}\]                      

    B)            \[\frac{3}{2}\]                      

    C)            3    

    D)            5

    Correct Answer: C

    Solution :

                       Apparent weight \[=V(\rho -\sigma )g=\frac{m}{\rho }(\rho -\sigma )g\]                    where  \[m=\]  mass of the body,                    \[\rho =\] density of the body                     \[\sigma =\] density of water                    If two bodies are in equilibrium then their apparent weight must be equal.                    \[\therefore \] \[\frac{{{m}_{1}}}{{{\rho }_{1}}}({{\rho }_{1}}-\sigma )=\frac{{{m}_{2}}}{{{\rho }_{2}}}({{\rho }_{2}}-\sigma )\]                    Þ    \[\frac{36}{9}(9-1)=\frac{48}{{{\rho }_{2}}}({{\rho }_{2}}-1)\]            By solving we get \[{{\rho }_{2}}=3\].


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