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Friday, 9 October

JEE Main 2021 · PhysicsMultiple choiceAssertion–reasonEasyConceptual

JEE Main 25 July 2021, Shift 1, Physics Q15

Question 15 of 90 in this shift, Physics question 15 of 30, Section 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 IxI_x, IyI_y & IzI_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 :
  1. (1)Both A and R are correct and R is the correct explanation of A.
  2. (2)Both A and R are correct but R is NOT the correct explanation of A.
  3. (3)A is correct but R is not correct.
  4. (4)A is not correct but R is correct.Official answer

Official answer

Option 4

NTA final key.

Chapter
System of Particles and Rotational Motion
Topic
Moment of Inertia
Idea tested
Radius of Gyration

Same topic in other shifts

All Moment of Inertia questions
  1. 2 Apr 2026, Shift 2 · Q50Moment of inertia about an axis ABAB for a rod of mass 40 kg and length 3 m is same as that of a solid sphere of mass of 10 kg and radius…MediumNumerical valueHas a figure
  2. 4 Apr 2026, Shift 1 · Q30A solid sphere of mass MM and radius RR is divided into two unequal parts. The smaller part having mass M/8M/8 is converted into a sphere…MediumSingle correct
  3. 6 Apr 2026, Shift 1 · Q31A solid sphere of radius 4 cm and mass 5 kg is rotating (rotation axis is passing through the centre of the sphere) with an angular…MediumSingle correct
  4. 2 Apr 2025, Shift 1 · Q32Moment of inertia of a rod of mass 'M' and length 'L' about an axis passing through its center and normal to its length is 'α\alpha'. Now…MediumSingle correct
  5. 2 Apr 2025, Shift 2 · Q28The moment of inertia of a circular ring of mass MM and diameter rr about a tangential axis lying in the plane of the ring is :EasySingle correct
  6. 7 Apr 2025, Shift 1 · Q46A, B and C are disc, solid sphere and spherical shell respectively with same radii and masses. These masses are placed as shown in figure.…HardNumerical valueHas a figure

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.