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

  • question_answer
    Let the moment of inertia of a hollow cylinder of length 30 cm (inner radius 10 cm and outer radius 20 cm), about its axis be I. The radius of a thin cylinder of the same mass such that its moment of inertia about its axis is also J, is [JEE Main Online Paper Held On 12-Jan-2019 Morning]

    A) 14 cm                          

    B) 16 cm

    C) 12 cm              

    D)   18 cm

    Correct Answer: B

    Solution :

    \[\frac{mR_{1}^{2}+R_{2}^{2}}{2}=m{{K}^{2}}\] \[\frac{m({{10}^{2}}+{{20}^{2}})}{2}=m{{K}^{2}}\Rightarrow \frac{100+400}{2}={{K}^{2}}\] \[{{K}^{2}}=250\] \[\Rightarrow K\,\underline{\approx }\,16\,cm\]


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