KVPY Sample Paper KVPY Stream-SX Model Paper-28

  • question_answer
    A cylindrical plastic bottle of negligible mass of filled with 310 ml of water and left floating in a pond with still water. If pressed downward slightly and released, it starts performing simple harmonic motion at angular frequency co. If the radius of the bottle is 2.5 cm then co is close to: (density of water\[={{10}^{3}}kg/{{m}^{3}}\])

    A) \[3.75\text{ }rad\text{ }{{s}^{-1}}\]

    B) \[1.25\text{ }rad\text{ }{{s}^{-1}}\]

    C) \[2.50\text{ }rad\text{ }{{s}^{-1}}\]       

    D) \[5.00\text{ }rad\text{ }{{s}^{-1}}\]

    Correct Answer: B

    Solution :

    \[A\rho gx={{F}_{restoring}}\]
    \[\pi {{r}^{2}}\rho gx=n{{\omega }^{2}}x\]
    \[\therefore \]      \[\omega \sqrt{\frac{\pi {{r}^{2}}\rho g}{\rho v}}\]
    \[=r\sqrt{\frac{\pi g}{v}}\]
    \[=2.5\times {{10}^{-2}}\sqrt{\frac{3.14\times 10}{310\times {{10}^{-6}}}}\]
    \[=2.5\times {{10}^{-2}}\times {{10}^{2}}\sqrt{10}\]
    \[\omega =2.5\times \sqrt{10}\]
    \[\therefore \]      \[f=\frac{2.5\times \sqrt{10}}{2\pi }\]
    \[=1.25.\]


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