JEE Main & Advanced Sample Paper JEE Main - Mock Test - 3

  • question_answer
    Let \[\bar{v},\] \[{{v}_{rms}}\] and \[{{v}_{p}}\] respectively denote the mean speed, root mean square speed and most probable speed of the molecules in an ideal monatomic gas at absolute temperature T. The mass of a molecule is m. Then

    A) No molecule can have speed greater than \[\sqrt{2}{{v}_{rms}}\]

    B) No molecule can have speed less than \[{{v}_{p}}/\sqrt{2}\]

    C) \[{{v}_{p}}=\bar{v}<{{\bar{v}}_{rms}}\]

    D) The average kinetic energy of a molecule is \[\frac{3}{4}mv_{p}^{2}\]

    Correct Answer: D

    Solution :

    \[{{v}_{rms}}=\sqrt{\frac{3RT}{M}},\,\,{{v}_{P}}=\sqrt{\frac{2RT}{M}}=0.816\,{{v}_{rms}}\] \[\bar{v}=\sqrt{\frac{8RT}{\pi M}}=0.92{{\upsilon }_{rms}}\Rightarrow {{v}_{P}}<\bar{v}<{{\bar{v}}_{rms}}\] Further \[{{E}_{av}}=\frac{1}{2}mv_{rms}^{2}=\frac{1}{2}m\frac{3}{2}v_{P}^{3}=\frac{3}{4}mv_{P}^{2}\]


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