A triangular plate of uniform thickness and density is made to rotate about an axis perpendicular to the plane of the paper (a) passing through A,(b) passing through B, by the application of the same force F, at C (mid-point of AB) as shown. Now,

τ=Fl2 is same in magnitude for both cases.Also, τ=IαSo, Iα is constant.Moment of Inertia is a quantity to measure how mass is distributed about the axis. Since, mass of plate is distributed far away from point A , MOI about axis passing through A is larger compared to point B. For case (b), I is small. So, α is large