Manipal Engineering Manipal Engineering Solved Paper-2010

  • question_answer
    A gas is suddenly expanded such that its final volume becomes 3 times its initial volume. If the specific heat at constant volume of the gas is 2R, then the ratio of initial to final pressures is nearly equal to

    A)  5                                            

    B)  6.5

    C)  7                            

    D)         3.5

    Correct Answer: A

    Solution :

    As gas is suddenly expanded so it is an adiabatic process, \[ie\],    \[p{{V}^{\gamma }}=\]constant or            \[{{p}_{1}}V_{1}^{\gamma }={{p}_{2}}V_{2}^{\gamma }\] Given \[{{V}_{2}}=3{{V}_{1}},\,\,{{C}_{V}}=2R\] \[\therefore \]  \[{{C}_{p}}=2R+R=3R\] \[\Rightarrow \]               \[\gamma =\frac{{{C}_{p}}}{{{C}_{V}}}=\frac{3R}{2R}=1.5\] \[\therefore \]  \[\frac{{{p}_{1}}}{{{p}_{2}}}={{\left( \frac{{{V}_{2}}}{{{V}_{1}}} \right)}^{\gamma }}={{(3)}^{1.5}}=5.1\approx 5\]


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