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Friday, 9 October

JEE Main 2025 · PhysicsNumerical answerNumerical valueMediumCalculation

JEE Main 7 April 2025, Shift 2, Physics Q46

Question 46 of 75 in this shift, Physics question 21 of 25, Section B.

MM and RR be the mass and radius of a disc. A small disc of radius R3\frac{R}{3} is removed from the bigger disc as shown in figure. The moment of inertia of remaining part of bigger disc about an axis ABAB passing through the centre OO and perpendicular to the plane of disc is 4xMR2\frac{4}{x}MR^2. The value of xx is __________.

The figure, in words

Large disc of radius R with centre O and vertical axis AB through O (A at top, B at bottom); a small circular hole of radius R/3 with centre O' lies on the horizontal line through O, on the left side, touching the left edge of the disc.

Official answer

9

NTA final key.

Chapter
System of Particles and Rotational Motion
Topic
Moment of Inertia
Idea tested
MOI of Bodies with Cavities

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. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.