Now click on the time line at the position that reads '50', which will move the current frame to 50. At exactly half the animation time (50th frame) we want the ball to hit the table's top surface. So we need to set a key frame at that frame in Maya. Move the ball to a position as shown in the image (make sure that the ball hits almost near the center of the table. Also take a look at the persp panel in Maya to check the position of the ball along the other axes too).

Now press the 's' key to set a key frame of the ball's position at the 50th frame. You will notice the key frame indicator (vertical red line) in Maya in the time-line at the current frame's position.