BCECE Engineering BCECE Engineering Solved Paper-2012

  • question_answer
    If the height of a mercury barometer is 75 cm at sea level and 50 cm at the top of a hill and the ratio of density of mercury to that of air is \[{{10}^{4}}\] then the height of the hill is

    A)  1.25 km              

    B)         2.5 km

    C)  250 m                  

    D)                         750 m

    Correct Answer: B

    Solution :

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


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