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

  • question_answer
    A hemispherical bowl just floats without sinking in a liquid of  density 1.2 × 103kg/m3. If outer diameter and the density of the bowl are 1 m and 2 × 104 kg/m3 respectively, then the inner diameter of the bowl will be                 [SCRA 1998]

    A)            0.94 m                                     

    B)            0.97 m                                     

    C)            0.98 m                                     

    D)            0.99 m

    Correct Answer: C

    Solution :

                       Weight of the bowl = mg                    = \[V\rho g\]\[=\frac{4}{3}\pi \left[ {{\left( \frac{D}{2} \right)}^{3}}-{{\left( \frac{d}{2} \right)}^{3}} \right]\rho g\] where D = Outer diameter , d = Inner diameter \[\rho \] = Density of bowl                                  Weight of the liquid displaced by the bowl \[=V\sigma g\]\[=\frac{4}{3}\pi {{\left( \frac{D}{2} \right)}^{3}}\sigma \,g\] where \[\sigma \] is the density of the liquid.                                 For the flotation  \[\frac{4}{3}\pi {{\left( \frac{D}{2} \right)}^{3}}\sigma g=\frac{4}{3}\pi \left[ {{\left( \frac{D}{2} \right)}^{3}}-{{\left( \frac{d}{2} \right)}^{3}} \right]\rho g\]                                 Þ \[{{\left( \frac{1}{2} \right)}^{3}}\times 1.2\times {{10}^{3}}=\left[ {{\left( \frac{1}{2} \right)}^{3}}-{{\left( \frac{d}{2} \right)}^{3}} \right]\,2\times {{10}^{4}}\] By solving we get d = 0.98 m.


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