BHU PMT BHU PMT Solved Paper-2003

  • question_answer
    When temperature of an ideal gas is increased from 27°C to 277°C, its rms speed is changed from 400 m/s to\[{{v}_{s}}\]. The \[{{v}_{s}}\] is:                                                                                                                                           [BHU M-2003]

    A)  \[516\,\,m/s\]                 

    B)  \[450\,\,m/s\]

    C)  \[310\,\,m/s\]                 

    D)  \[746\,\,m/s\]

    Correct Answer: A

    Solution :

                     The root mean square velocity of the gas is given by                                 \[{{v}_{rms}}=\sqrt{\frac{3RT}{M}}\] Where \[R\] is gas constant, \[T\] is absolute temperature and \[M\] is the molecular weight of the gas.                                 \[{{T}_{1}}=27{{\,}^{\circ }}C=273+27=300\,K\]                                 \[{{T}_{2}}=227{{\,}^{\circ }}C=273+227=500\,K\]                 \[\therefore \]                  \[\frac{{{v}_{1}}}{{{v}_{2}}}=\sqrt{\frac{300}{500}=\sqrt{\frac{3}{5}}}\] Given, \[{{v}_{1}}=400\,m/s,\,{{v}_{2}}={{v}_{s}}\]                 \[\therefore \]                  \[{{v}_{s}}=\sqrt{\frac{5}{3}}\times 400\]                                                 \[=1.29\times 400\]                                                 \[=516.39\,m/s\approx 516\,m/s\] Note: If the absolute temperature of the gas becomes zero, then the motion of molecules will cease.


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