JEE Main & Advanced JEE Main Online Paper (Held On 08 April 2018)

  • question_answer
    A solid sphere of radius r made of a soft material of bulk modulus K is surrounded by a liquid in a cylindrical container. A massless piston of area a floats on the surface of the liquid, covering entire cross section of cylindrical container. When a mass m is placed on the surface of the piston to compress the liquid, the fractional decrement in the radius of the sphere, \[\left( \frac{dr}{r} \right),\]is:                   [JEE Main Online 08-04-2018]

    A)  \[\frac{\text{mg}}{\text{3}\,\,\text{Ka}}\]                

    B)  \[\frac{mg}{Ka}\]

    C)  \[\frac{Ka}{mg}\]                              

    D)  \[\frac{Ka}{3\,\,mg}\]

    Correct Answer: A

    Solution :

    \[K=\frac{mg/a}{\frac{\Delta V}{V}}\] and \[V=\frac{4}{3}\pi {{r}^{3}}\] \[\therefore \frac{\Delta V}{V}=3\frac{dr}{r}\] So, \[K=\frac{mg/a}{3\frac{dr}{r}}\Rightarrow \frac{dr}{r}=\frac{mg}{3Ka}\]


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