JEE Main & Advanced AIEEE Solved Paper-2004

  • question_answer
    One solid sphere A and another hollow sphere B are of same mass and same outer radii. Their moment of inertia about their diameters are respectively \[{{l}_{A}}\] and \[{{l}_{B}}\] such that

    A) \[{{l}_{A}}={{l}_{B}}\]    

    B)        \[{{l}_{A}}>{{l}_{B}}\]    

    C)        \[{{l}_{A}}<{{l}_{B}}\]    

    D)        \[\frac{{{l}_{A}}}{{{l}_{B}}}\,=\frac{{{d}_{A}}}{{{d}_{B}}}\] where\[{{d}_{A}}\]and\[{{d}_{B}}\]are their densities.

    Correct Answer: C

    Solution :

    Let same mass and same outer radii of solid sphere and hollow sphere are M and R, respectively. The moment of inertia of solid sphere A about its diameter \[{{l}_{A}}=\frac{2}{5}\,M{{R}^{2}}\]                          ...(i) Similarly, the moment of inertia of hollow sphere (spherical shell) B about its diameter \[{{l}_{B}}=\frac{2}{3}\,M{{R}^{2}}\]                       ...(ii) It is clear from Eqs. (i) and (ii), \[{{l}_{A}}<{{l}_{B}}\]. Alternatively We can say that the object which has mass at greater distance will have higher moment of inertia as \[l=m{{r}^{2}}\]. So, hollow sphere (B) has large\[l\], because it has mass only on its circumference.


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