JEE Main & Advanced JEE Main Paper (Held On 15 April 2018) Slot-I

  • question_answer
    A body of mass \[M\] and charge \[q\] is connected to a spring of spring constant\[k\]. It is oscillating along x-direction about its equilibrium position, taken to be at \[x=0\], with an amplitude \[A\]. An electric field \[E\] is applied along the x-direction. Which of the following statements is correct? [JEE Online 15-04-2018]

    A) The total energy of the system is \[\frac{1}{2}m{{\omega }^{2}}{{A}^{2}}+\frac{1}{2}\frac{{{q}^{2}}{{E}^{2}}}{k}\]

    B) The new equilibrium position is at a distance: \[\frac{2qE}{k}\] from \[x=0\]

    C) The new equilibrium position is at a distance:\[\frac{qE}{2k}\]  from \[x=0\]

    D) The total energy of the system is\[\frac{1}{2}m{{\omega }^{2}}{{A}^{2}}-\frac{1}{2}\frac{{{q}^{2}}{{E}^{2}}}{k}\]

    Correct Answer: A

    Solution :

    When electric field is applied, at equilibrium \[F=kx=qE\] \[x=\frac{qE}{k},x-extension\,\,of\,\,spring\] Total Energy of system = Kinetic energy + Potential energy \[T.E.=\frac{1}{2}m{{v}^{2}}+\frac{1}{2}k{{x}^{2}}\] \[=\frac{1}{2}\frac{{{q}^{2}}{{E}^{2}}}{k}+\frac{1}{2}m{{\omega }^{2}}{{A}^{2}}\]


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