1. The problem statement, all variables and given/known data Three particles, each with mass m = 0.5 kg, are fixed on a uniform circular ring of mass M = 2 kg, radius a = 0.6 m and centre O, to form the corners of an equilateral triangle. What is the moment of inertia of this system? 2. Relevant equations I = Σma2 3. The attempt at a solution I = 3(2 x 0.62) = 2.16 kgm2 I'm confused because it is either that or zero and I can never tell when it is zero. Thank you.