JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity / द्रव यांत्रिकी, भूतल तनाव और चिपचिपापन Question Bank Pascal's Law and Archimedes Principle

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    In making an alloy, a substance of specific gravity \[{{s}_{1}}\] and mass \[{{m}_{1}}\] is mixed with another substance of specific gravity \[{{s}_{2}}\] and mass \[{{m}_{2}}\]; then the specific gravity of the alloy is       [CPMT 1995]

    A)            \[\left( \frac{{{m}_{1}}+{{m}_{2}}}{{{s}_{1}}+{{s}_{2}}} \right)\]     

    B)            \[\left( \frac{{{s}_{1}}{{s}_{2}}}{{{m}_{1}}+{{m}_{2}}} \right)\]        

    C)            \[\frac{{{m}_{1}}+{{m}_{2}}}{\left( \frac{{{m}_{1}}}{{{s}_{1}}}+\frac{{{m}_{2}}}{{{s}_{2}}} \right)}\]              

    D)            \[\frac{\left( \frac{{{m}_{1}}}{{{s}_{1}}}+\frac{{{m}_{2}}}{{{s}_{2}}} \right)}{{{m}_{1}}+{{m}_{2}}}\]

    Correct Answer: C

    Solution :

                       Specific gravity of alloy \[=\frac{Density of alloy}{\text{Density of water}}\]                                 \[=\frac{\text{Mass of alloy }}{\text{Volume of alloy}\times \text{density of water  }}\] \[=\frac{{{m}_{1}}+{{m}_{2}}}{\left( \frac{{{m}_{1}}}{{{\rho }_{1}}}+\frac{{{m}_{2}}}{{{\rho }_{2}}} \right)\times {{\rho }_{w}}}\]\[=\frac{{{m}_{1}}+{{m}_{2}}}{\frac{{{m}_{1}}}{{{\rho }_{1}}/{{\rho }_{w}}}+\frac{{{m}_{2}}}{{{\rho }_{2}}/{{\rho }_{w}}}}=\frac{{{m}_{1}}+{{m}_{2}}}{\frac{{{m}_{1}}}{{{s}_{1}}}+\frac{{{m}_{2}}}{{{s}_{2}}}}\]  \[\left[ \text{As specific gravity of substance }=\frac{\text{density of substance }}{\text{density of water}} \right]\]


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