After the ball leaves the woman's hand, the only relevant force acting on the ball is the gravity, which produces an acceleration of a=g=9.81 m/s^2 on the baseball, directed downward. Gravity acts on the ball for the whole duration of the motion, so the acceleration of the ball is at every point of the motion, and therefore also when the baseball is at its highest point.
C) </span><span>T = 2 pi √ ( L / g ) </span> <span>0.57 = 2 x 3.14 x √ ( 0.2 / g ) </span><span> g = 25.5 m/s² </span> Hope this helps a little at least.. :)
