Verified Solution • 2025–26 Session
moderate
QJEEM21Ph5fa8: JEE Main 2021 Physics - Class 11 JEEM21Ph5fa8 Solution: Given below are two statements : one is labelled as Assertion A …
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 'M' and radius 'R' about X, Y axes (passing through its plane) and Z-axis which is perpendicular to its plane were found to be Ix, Iy and Iz respectively. The respectively 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 :
Assertion A : Moment of inertia of a circular disc of mass 'M' and radius 'R' about X, Y axes (passing through its plane) and Z-axis which is perpendicular to its plane were found to be Ix, Iy and Iz respectively. The respectively 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 :
Multiple Choice Options
- A Both A and R are correct but R is NOT the correct explanation of A.
- B A is not correct but R is correct.
- C A is correct but R is not correct.
- D Both A and R are correct and R is the correct explanation of A.
Step-by-Step Verified Solution
Iz = Ix + Iy (using perpendicular axis theorem) & I = mk2 (K : radius of gyration)
so, mKz2 = mKx2 + mKy2
Kz2 = Kx2 + Ky2
so radius of gyration about axes x, y & z won't be same hence assertion A is not correct reason R is correct statement (property of a rigid body)
so, mKz2 = mKx2 + mKy2
Kz2 = Kx2 + Ky2
so radius of gyration about axes x, y & z won't be same hence assertion A is not correct reason R is correct statement (property of a rigid body)