1. The problem statement, all variables and given/known data Calculate the moment of inertia of a uniform rigid rod of length L and mass M, about an axis perpendicular to the rod through one end. 2. Relevant equations Parallel axis theorem: I = Icm + MD2 Long thin rod with rotation axis through centre: Icm = 1/12 ML2 Long thin rod with rotation axis through end: I = 1/3 ML2 3. The attempt at a solution I know this is a straightforward substitution problem into the parallel axis theorem EQN. However, for this question, I'm not sure why the answer key uses Icm of the rotation axis through the CENTRE. The question specifically states that the rotation axis is at the end.... The answer given is I = 1/3ML2; I have calculated I = 7/12ML2, using the Icm of a long thin rod with the rotation axis through the end. Calculations: D = 1/2L, since the centre of mass of a rod is right down the middle I = Icm + MD2 I = 1/3 ML2 + M(1/2L)2 I = 7/12ML2 To reiterate, I'm just confused about why Icm was used for am axis through the centre, rather than through the end.