CMC Medical CMC-Medical VELLORE Solved Paper-2013

  • question_answer
    Root mean square speed of\[{{N}_{2}}(g)\]in air is \[515\,m{{s}^{-1}}.\] What is the average speed of He gas in the same air?

    A)  \[536.8\,m{{s}^{-1}}\]                  

    B)  \[839.2\,m{{s}^{-1}}\]

    C)  \[1245.5\,m{{s}^{-1}}\]                

    D)  \[1255.3\,m{{s}^{-1}}\]

    Correct Answer: D

    Solution :

                    \[{{u}_{rms}}=\sqrt{\frac{3RT}{M({{N}_{2}})}}\] \[{{\overline{u}}_{avg}}=\sqrt{\frac{8RT}{\pi {{M}_{(He)}}}}\] Both are at same temperature \[\frac{\overline{u\,}(He)}{{{U}_{rms}}({{N}_{2}})}=\sqrt{\frac{8M({{N}_{2}})}{3\pi {{M}_{(He)}}}}\] \[=\sqrt{\frac{8\times 28\times {{10}^{-3}}}{3\pi \times 4\times {{10}^{-3}}}}=2.4375\] \[\overline{u\,}(He)=2.4375\times 515=1255.3\,m{{s}^{-1}}\]


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