A disc of mass M and radius R is rolling with angular speed ω on a horizontal plane .The
magnitude of angular momentum of the disc about the origin O is
(a) 1/2 MR^2 W
(b) MR^2 W
Angular momentum = Linear momentum x Perpendicular distance.
Now the perpendicular distance, is the radius of the disc and angular momentum required is the angular momentum of the disc at the point of contact.
Hence MI about origin = MR2/2 + MR2 = 3MR2 /2
and Angular Momentum = 3MR2w/2