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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceDiagram basedMediumMulti-step

JEE Main 26 August 2021, Shift 2, Physics Q10

Question 10 of 90 in this shift, Physics question 10 of 30, Section A.

The solid cylinder of length 80 cm and mass M has a radius of 20 cm. Calculate the density of the material used if the moment of inertia of the cylinder about an axis CD parallel to AB as shown in figure is 2.7 kg m2^2.

The figure, in words

Vertical solid cylinder labelled M, length L marked by a double arrow on its left, radius r marked at the bottom base from the left edge to point B at the centre; axis AB drawn through the centre from point A (top) to point B (bottom); a parallel vertical line CD (C at top, D at bottom) to the right of the cylinder, with the distance between AB and CD marked L/2.
  1. (1)14.9 kg/m3^3
  2. (2)1.49×1021.49\times10^{2} kg/m3^3Official answer
  3. (3)7.5×1017.5\times10^{1} kg/m3^3
  4. (4)7.5×1027.5\times10^{2} kg/m3^3

Official answer

Option 2

NTA final key.

Chapter
System of Particles and Rotational Motion
Topic
Moment of Inertia
Idea tested
Parallel Axis Theorem

Same idea in other shifts

Asked 7× in all
  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. 31 Jan 2024, Shift 2 · Q52Two identical spheres each of mass 2 kg and radius 50 cm are fixed at the ends of a light rod so that the separation between the centers…MediumNumerical value
  3. 27 Aug 2021, Shift 1 · Q2Moment of inertia of a square plate of side ll about the axis passing through one of the corner and perpendicular to the plane of square…EasySingle correct
  4. 31 Aug 2021, Shift 2 · Q14A system consists of two identical spheres each of mass 1.5 kg and radius 50 cm at the ends of a light rod. The distance between the…MediumSingle correct
  5. 26 Feb 2021, Shift 1 · Q5Four identical solid spheres each of mass ‘m’ and radius ‘a’ are placed with their centres on the four corners of a square of side ‘b’.…MediumSingle correct
  6. 4 Sep 2020, Shift 2 · Q5For a uniform rectangular sheet shown in the figure, the ratio of moments of inertia about the axes perpendicular to the sheet and passing…EasyDiagram basedHas 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 108 of the 174 JEE Main shifts held from 2017 to 2026.