AMU Medical AMU Solved Paper-2011

  • question_answer
    The moment of inertia of a thin square plate ABCD (shown in figure below) of uniform thickness about an axis passing through the centre 0 and perpendicular to the plane of the plate is

    A)  \[{{I}_{1}}-{{I}_{2}}\]  

    B)  \[{{I}_{1}}+{{I}_{2}}+{{I}_{3}}+{{I}_{4}}\]

    C)  \[{{I}_{1}}+{{I}_{3}}\]    

    D)  \[{{I}_{1}}+{{I}_{4}}\]                

    Correct Answer: A

    Solution :

    (a,c,d) Applying the theorem of perpendicular axis                                 \[I={{I}_{1}}+{{I}_{2}}={{I}_{3}}+{{I}_{4}}\]                 Because of symmetry, we have                                 \[{{I}_{1}}={{I}_{2}}\] and \[{{I}_{3}}={{I}_{4}}\]                 Hence, \[I=2{{I}_{1}}=2{{I}_{2}}=2{{I}_{3}}=2{{I}_{4}}\]                 or            \[{{I}_{1}}={{I}_{2}}={{I}_{3}}={{I}_{4}}\]                 ie, sum of two moment of inertia of square plate about any axis in a plane (passing through centre) should be equal to moment of inertia about the axis passing through the centre ad perpendicular to the plane of the plate.                                


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