Equations of Motion in Free Fall

We shall take as our reference frame a frame rigidly attached to the earth. The y-axis will be taken as positive vertically upward. Then the acceleration due to gravity g will be a vector pointing vertically down (toward the center of earth ) in the negative y direction. Our equations for constant acceleration are applicable here. Then
v=vo+at,
y =[(vo+v)/2].t,
y = vot+0.5at^2
v^2=vo^2+2ay

and put a =-g for problems in free fall. Here y =0 at t =0 , and g is the magnitude of acceleration due to gravity, 9.80 meters/sec^2