Question

# Three identical thin rods each of mass m and length L are joined together to form an equilateral triangular frame. The moment of inertia of frame about an axis perpendicular to the plane of frame and passing through a corner is:

A
2mL23
B
3mL22
C
4mL23
D
3mL24
Solution
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#### Sum of MI of the two rods, at vertex of which the axis passes, is 2×mL2/3=2mL2/3For the third rod, the distance between center of the rod and the axis is d=√3L/2Using parallel axis theorem, its MI is mL2/12+3mL2/4=5mL2/6So total MI of the system is 2mL2/3+5mL2/6=3mL2/2 0
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