Railways NTPC (Technical Ability) Engineering Mechanics and Strength of Materials Question Bank Engineering Mechanics

  • question_answer
    A circular disc rolls without slip on an inclined plane. The ratio of its rotational kinetic energy to the total energy is:

    A) \[\frac{1}{4}\]                          

    B) \[\frac{1}{2}\]

    C) \[\frac{1}{3}\]                          

    D) \[\frac{2}{3}\]

    Correct Answer: C

    Solution :

    Translation kinetic energy, \[{{K}_{1}}=\frac{1}{2}\,\,m{{v}^{2}}\] \[=\frac{1}{2}\,\,m\,{{r}^{2}}\times {{\omega }^{2}}\] Rational kinetic energy, \[{{K}_{2}}=\frac{1}{2}\,\,I\,{{\omega }^{2}}\] \[=\frac{1}{2}\times \frac{1}{2}m\,{{r}^{2}}\,\,{{\omega }^{2}}=\frac{1}{2}m\,{{r}^{2}}{{\omega }^{2}}\] Total kinetic energy, \[K={\scriptstyle{}^{3}/{}_{4}}m{{r}^{2}}{{\omega }^{2}}\] \[\frac{{{K}_{2}}}{K}=\frac{1}{4}\times \frac{4}{3}=\frac{1}{3}\]


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