4. at ti = 0 a ball is thrown straight upward from yi = 0 at an initial speed vi. while in the air it is in free fall. (a) sketch ay-t, vy-t and y-t graphs for the motion (b) what are the magnitude and direction of the acceleration while the boulder is  moving upward?  moving downward?  at the highest point? (c) when is the velocity of the ball zero? (d) find the maximum height ymax reached by the ball. (e) find the time at which the ball reaches this maximum height. (f) at what time is the ball moving at vi/2 upward? (g) at what time is it moving at vi/2 downward? (h) at what time does the ball return to its initial position? (i) how long is the ball in the air above some arbitrary height h? (j) check that your answer for (i) makes sense. if you set the height to h = 0, you should get the same answer as for part (h). if you set the height to h = ymax you should get δt = 0.