JEE Main & Advanced JEE Main Paper (Held On 12-Jan-2019 Evening)

  • question_answer
    A simple harmonic motion is represented by \[y=5(sin3\pi t+\sqrt{3}cos3\pi t)cm\] The amplitude and time period of the motion are [JEE Main Online Paper Held On 12-Jan-2019 Evening]

    A) \[5cm,\frac{3}{2}s\]                              

    B) \[10cm,\frac{2}{3}s\]

    C) \[5cm,\frac{2}{3}s\]                  

    D)   \[10cm,\frac{3}{2}s\]

    Correct Answer: B

    Solution :

    The given equation is y = 5            \[(sin3\pi t+\sqrt{3}cos3\pi t)\]                             \[\Rightarrow \]\[y=2\times 5\left( \frac{1}{2}\sin 3\pi t+\frac{\sqrt{3}}{2}\cos 3\pi t \right)\] \[=10\left( \cos \frac{\pi }{3}\sin 3\pi t+\sin \frac{\pi }{3}\cos 3\pi t \right)\] \[y=10\sin \left( 3\pi t+\frac{\pi }{3} \right)\]                                 ?.(i) Comparing eqn. (i) with standard equation \[y=A\sin (\omega t+\phi )\] \[\Rightarrow \]\[\omega =3\pi \]and \[A=10cm\] \[\therefore \]Time period \[T=\frac{2\pi }{\omega }=\frac{2}{3}s\]


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