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

  • question_answer
    The height of a mercury barometer is 75 cm at sea level and 50 cm at the top of a hill. Ratio of density of mercury to that of air is 104. The height of the hill is

    A)            250 m                                      

    B)            2.5 km

    C)            1.25 km                                  

    D)            750 m

    Correct Answer: B

    Solution :

                       Difference of pressure between sea level and the top of hill DP\[=({{h}_{1}}-{{h}_{2}})\times {{\rho }_{Hg}}\times g\]\[=(75-50)\times {{10}^{-2}}\times {{\rho }_{Hg}}\times g\]   ?(i)                                 and pressure difference due to h meter of air                                  DP =\[h\times {{\rho }_{air}}\times g\]                                   ?(ii)                                 By equating (i) and (ii) we get                                 \[h\times {{\rho }_{air}}\times g=(75-50)\times {{10}^{-2}}\times {{\rho }_{Hg}}\times g\]                                 \[\therefore \ h=25\times {{10}^{-2}}\left( \frac{{{\rho }_{Hg}}}{{{\rho }_{air}}} \right)\]\[=25\times {{10}^{-2}}\times {{10}^{4}}=2500\,m\]            \ Height of the hill = 2.5 km.


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