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NEET
Exam
NEET
Subject
Physics
Chapter
Rotational Motion

NEET · Physics · Rotational Motion

Given below are two statements: one is labelled as Assertion A and...

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: Moment of inertia of a circular disc of mass MM and radius RR about X,YX, Y axes (passing through its plane) and Z-axis which is perpendicular to its plane were found to be Ix,Iy{I}_{x}, {I}_{y} and Iz{I}_{z}, respectively. The respective radii of gyration about all the three axes will be the same.

Reason R: A rigid body making rotational motion has fixed mass and shape. In the light of the above statements, choose the most appropriate answer from the options given below:

Options

  1. ABoth A and R are correct but R is not the correct explanation of A.
  2. BA is not correct but R is correct.
  3. CA is correct but R is not correct.
  4. DBoth A and R are correct and R is the correct
    explanation of A.

Correct answer

B. A is not correct but R is correct.

Step-by-step solution

Iz=Ix+Iy{I}_{z} = {I}_{x} + {I}_{y} (using perpendicular axis theorem)

and I=mk2(K:I = m{k}^{2} ( K: radius of gyration) 

so mKz2=mKx2+mKy2m{K}_{z}^{2} = m{K}_{x}^{2} + m{K}_{y}^{2}

Kz2=Kx2+Ky2{K}_{z}^{2} = {K}_{x}^{2} + {K}_{y}^{2}

So radius of gyration about axes x,yx, y and zz will not be same, hence assertion A is not correct reason R is correct statement (property of a rigid body).

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