BCECE Medical BCECE Medical Solved Papers-2003

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

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

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

    C)  \[2.5\,\,km{{s}^{-1}}\]

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

    Correct Answer: D

    Solution :

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


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