A thin uniform rod (X) of mass M and length L is pivoted at a height ( L 3 ) as shown in the figure. The rod is allowed to fall from a vertical…
JEE Main 2026 — Physics Mechanics
2026mcqmedium
A thin uniform rod (X) of mass M and length L is pivoted at a height (3L) as shown in the figure. The rod is allowed to fall from a vertical position and lie horizontally on the table. The angular velocity of this rod when it hits the table top, is ____. (g= gravitational acceleration)
Official previous-year question
Held on 24 Jan 2026 · Verified 6 Jul 2026.
Options
A
23Lg
B
21Lg
C
23Lg
D
L3g
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Solution
The rod is pivoted at a distance 3L from one end. The centre of mass is at a distance 6L from the pivot.
Using energy conservation:
mg6ℓ=21Iω2
Moment of inertia about the pivot (using parallel axis theorem):
I=12mℓ2+m(6ℓ)2=12mℓ2+36mℓ2=9mℓ2
mg6ℓ=21⋅9mℓ2⋅ω2
ω2=6⋅2ℓ9g=ℓ3g
ω=ℓ3g
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