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JEE Main 9 January 2020, Shift 1, Physics Q4

Question 4 of 75 in this shift, Physics question 4 of 25, Section A.

Three solid spheres each of mass m and diameter d are stuck together such that the lines connecting the centres form an equilateral triangle of side of length d. The ratio

I_0/I_A

of moment of inertia

I_0

of the system about an axis passing the centroid and about center of any of the spheres

I_A

and perpendicular to the plane of the triangle is :

The figure, in words

Three circles labelled B, A and C, touching/overlapping one another, with a dot at the centre of each; the three centres are joined by straight lines forming a triangle. A small cross marks a point inside the triangle with an arrow from the label O pointing to it. A vertical double-headed arrow labelled d is drawn to the right of circle A, spanning the height of circle A.

(1) $\frac{13}{23}$ Official answer
(2) $\frac{13}{15}$
(3) $\frac{23}{13}$
(4) $\frac{15}{13}$

Official answer

Option 1

NTA final key (Jan 2020).

Chapter: System of Particles and Rotational Motion
Topic: Moment of Inertia
Idea tested: MOI of Composite Bodies

Same idea in other shifts

Asked 6× in all

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.