Moment of inertia about an axis AB 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 R about an…
JEE Main 2026 — Physics Mechanics
2026integermedium
Moment of inertia about an axis AB 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 R about an axis parallel to AB axis with separation of 3 m as shown in figure below. The value of R is given as 2α. The value of α is _______.
Official previous-year question
Held on 2 Apr 2026 · Verified 6 Jul 2026.
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Solution
Moment of inertia of the rod about axis AB passing through one of its ends:
Irod=3ML2=340×(3)2=340×9=120 kg⋅m2
Moment of inertia of the solid sphere about the same axis AB, using the parallel axis theorem I=Icm+md2:
Mass m=10 kg, radius R, distance from the centre of the sphere to axis AB is d=3 m.
Isphere=52mR2+md2=52(10)R2+10(3)2=4R2+90
Equating the two moments of inertia:
120=4R2+90
4R2=30
R2=215
R=215
Comparing with R=2α:
α=15
Hence, α=15.
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