(a) Before being brought in contact with the table the disc was in pure rotational motion (only) about its axis passing through centre –
∴ vcm = 0 as the point on axis are considered at rest.
(b) When the rotating disc is placed in contact with table’s surface due to friction, linear velocity of a point on the rim decreases.
(c) When disc is placed in contact with the surface of the table, due to frictional force, centre of mass acquires some linear velocity. The linear velocity increases.
(d) Frictional force
(e) When rolling of disc starts on table, then vcm = ωR due to reaction force.
(f) Acceleration produced in centre of mass due to reaction force F because of frictional force in disc
Angular retardation produced by the torque due to friction.
Here, frictional force helps in rolling motion.