Question

Three identical rods each of mass M, length l are joined to form an equilateral D ABC. Find the MOI about BC as shown

• A. $\frac { 2 } { 3 }$ Ml²
• B. $\frac { \mathrm { M } \ell ^ { 2 } } { 4 }$
• C. $\frac { \mathrm { M } \ell ^ { 2 } } { 2 }$
• D. None

Answer 1

Answer: (C)

$\frac { \mathrm { M } \ell ^ { 2 } } { 2 }$

Answer 2

I = I₁ + I₂ + I₃

= $\frac { M \left( \ell \sin 60 ^ { 0 } \right) ^ { 2 } } { 3 }$ + $\frac { M \left( \ell \sin 60 ^ { 0 } \right) ^ { 2 } } { 3 }$ + 0 = $\frac { \mathrm { M } \ell ^ { 2 } } { 2 }$