JEE Main & Advanced Sample Paper JEE Main Sample Paper-17

  • question_answer
    A particle moves in a straight line with retardation proportional to square of its displacement. Its loss of kinetic energy for any displacement x is proportional to

    A) \[{{x}^{2}}\]                                      

    B) \[{{x}^{3}}\]

    C) \[\ln \,x\]                                           

    D) \[{{e}^{x}}\]

    Correct Answer: B

    Solution :

    \[\frac{dv}{dt}=v\frac{dv}{dx}=-k{{x}^{2}}\] \[\Rightarrow \]               \[vdv=-k{{x}^{2}}dx\] Let \[{{v}_{1}}\]and \[{{v}_{2}}\]be the velocities of the particle at locations \[{{x}_{1}}\]and \[{{x}_{2}}k,\] respectively. Then \[\frac{v_{2}^{2}-v_{1}^{2}}{2}=-k\left[ \frac{x_{2}^{3}-x_{1}^{3}}{3} \right]\] \[\therefore \]  Loss in \[KE\propto {{x}^{3}}\]


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