Show that the sum HA of the moments about a point A of the moment of the particles of a rigid slab in plane motion is equal to IA ω, where ω is the angular velocity of the slab at the instant considered and IA is the moment of inertia of the slab about A, if and only if one of the following conditions is satisfied:

(a) A is the mass center of the slab,

(b) A is the instantaneous center of rotation,

(c) The velocity of A is directed along a line joining point A and the mass center G.