BCECE Engineering BCECE Engineering Solved Paper-2003

  • question_answer
    Four molecules of a gas have speeds 1, 2, 3 and \[4\,km{{s}^{-1}}\]. The value of ms speed of the gas molecules is:

    A) \[\frac{\text{1}}{\text{2}}\sqrt{\text{15}}\text{km}{{\text{s}}^{\text{-1}}}\]                      

    B)         \[\frac{\text{1}}{\text{2}}\sqrt{\text{10}}\text{km}{{\text{s}}^{\text{-1}}}\]

    C)         \[\text{2}\text{.5km}{{\text{s}}^{\text{-1}}}\]                                 

    D)        \[\sqrt{\frac{15}{2}}\text{km}{{\text{s}}^{\text{-1}}}\]

    Correct Answer: D

    Solution :

    The square root of \[{{\bar{v}}^{2}}\]is called the root mean square velocity (rms) speed of the molecules. \[{{v}_{rms}}=\sqrt{{{{\bar{v}}}^{2}}}\] \[=\sqrt{\frac{{{v}_{1}}^{2}+{{v}_{2}}^{2}+{{v}_{3}}^{2}+{{v}_{4}}^{2}}{4}}\] \[=\sqrt{\frac{{{(1)}^{2}}+{{(2)}^{2}}+{{(3)}^{2}}+{{(4)}^{2}}}{4}}\] \[=\sqrt{\frac{1+4+9+16}{4}}\] \[=\sqrt{\frac{30}{4}}\] \[=\sqrt{\frac{15}{2}}km{{s}^{-1}}\]


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