a wheel revolves

about a fixed horizontal axis through O (the center).
During a certain interval of time, the
angular velocity (which initially is 20 rad
per second clockwise) changes uniformly
at such a rate that the angular
displacement is 60 rad counterclockwise,
and the total angle turned through is 100
rad. Point A is in the position shown 2.5
sec after the beginning of the time
interval.
Determine, for this instant, the linear
acceleration of point A.