KVPY Sample Paper KVPY Stream-SX Model Paper-9

  • question_answer
    A fixed container is filled with a piston which is attached to a spring of spring constant k. The other end of the spring is attached to a rigid wall. Initially the spring is in its natural length and the length of container between the piston and its side wall.is L. Now an ideal diatomic gas is slowly filled in the container so that the piston moves quasistatically. If pushed the piston by x so that the spring now is compressed by x. The total rotation kinetic energy of the gas molecules in terms of the displacement x of the piston is (there is vacuum outside the container)

    A) \[k\times L\]

    B) \[4k\times L\]

    C) \[k\times (x+L)\]

    D) \[\frac{2k{{x}^{2}}}{L}\]

    Correct Answer: C

    Solution :

    Rotational K.E.\[=\]Rotational degree of freedom\[\times \frac{1}{2}nRT\]
    \[=2\times \frac{1}{2}nRT=nRT=PV\]
    \[=PA\cdot \frac{V}{A}=\] force on piston \[(L+x)\]
    \[=kx\,(L+x)\]


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