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Units And Measurement

Question
CBSEENPH11020743

The ratio of the radii of gyration of a circular disc to that of a circular ring, each of same mass and radius, around their respective axes is 

  • square root of 3 colon square root of 2
  • 1 colon square root of 2
  • square root of 2 colon 1
  • square root of 2 colon space square root of 3

Solution

B.

1 colon square root of 2

The square root of the ratio of the moment of inertia of rigid body nad its mass is called radius of gyration.
As in key idea, radius of gyration is given by
straight K space equals space square root of straight I over straight M end root
For space given space problem
straight K subscript disc over straight K subscript ring space equals space square root of straight I subscript disc over straight I subscript ring end root
But space straight I subscript disc space left parenthesis about space its space axis right parenthesis space equals space 1 half MR squared
and space straight I subscript ring space left parenthesis about space its space axis right parenthesis space equals MR squared
Where space straight R space is space the space the space radius space of space both space bodies.
Therefore comma space eq left parenthesis straight i right parenthesis space becomes
straight K straight K subscript disc over straight K subscript ring space equals space square root of fraction numerator begin display style 1 half end style MR squared over denominator MR squared end fraction end root space equals space 1 colon square root of 2