JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Oscillations

  • question_answer
    Starting from the origin a body oscillates simple harmonically with a period of 2 s. After what time will its kinetic energy be 75% of the total energy?        

    A) \[\frac{1}{6}s\] 

    B) \[\frac{1}{4}s\]

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

    D) \[\frac{1}{12}s\]

    Correct Answer: A

    Solution :

    [a] \[K.E.=\frac{1}{2}m{{a}^{2}}{{\omega }^{2}}{{\cos }^{2}}\omega t\] and \[T.E.=\frac{1}{2}m{{a}^{2}}{{\omega }^{2}}\] Given \[K.E.=0.75T.E.\] \[\Rightarrow \,0.75={{\cos }^{2}}\omega t\Rightarrow \omega t=\frac{\pi }{6}\] \[\Rightarrow \,t=\frac{\pi }{6\times \omega }\Rightarrow t=\frac{\pi \times 2}{6\times 2\pi }\Rightarrow t=\frac{1}{6}s\]


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