1. The problem statement, all variables and given/known data A ball is launched vertically upward from ground level with initial speed of 20 m/s. 1. How long is the ball in air? 2. What is the greatest height reached by the ball. 3. How many seconds after launch is the ball 15m above the release point. (Air resistance is negligible) The answers from the back of the book are: 1. 4.1 s 2. 20 m 3. 0.99 s and 3.1 s 2. Relevant equations Kinematic equations for constant acceleration: 1. vx = v0x + axt 2. vav x = 0.5(v0x + vx) 3. [tex]\Delta[/tex]x = v0xt + 0.5axt2 4. [tex]\Delta[/tex]x = 0.5(v0x + vx)t 3. The attempt at a solution Part 1 To find how long the ball is in the air - I need to find t (or 2t depending how you look at it) initial velocity is 20m/s and I am assuming final velocity to be zero. a is 9.8 So I used equation 1 above: So 0 = 20 + 9.8t => t=2.0408 (ignoring the sign) Hence 2t = 4.0816 (the total time ball is in the air) Is this correct, did the textbook round it up? Part 2 What is the greatest height reached by the ball? I use equation 4 above to find delta x: [tex]\Delta[/tex]x = 0.5(20+0)2.0408 I get 20.408 m Again is this correct, did the textbook round it up? Part 3 How many seconds after launch is the ball 15m above the release point? I am assuming we are given [tex]\Delta[/tex]x as 15m? I used equations 3 and 4 here but my answer is nowhere close. Can someone please help me. Thanks in advance Okay I don't know how to proceed here.