Question

Three identical rods each of mass $M$ , length $l$ are joined to form an equilateral $\Delta ABC$ . Find the Moment of Inertia about $BC$ as shown.

• A. $\frac{2}{3}Ml^{2}$
• B. $\frac{M l^{2}}{4}$
• C. $\frac{M l^{2}}{2}$
• D. none

Answer 1

Answer: (C)

$I=I_{1}+I_{2}+I_{3}=\frac{M\left(l \sin 60^{\circ}\right)^{2}}{3}+\frac{M\left(l \sin 60^{\circ}\right)^{2}}{3}+0=\frac{M l^{2}}{2}$