1. The problem statement, all variables and given/known data A ball is thrown straight up with an initial speed of 30m/s, (a) Show that the time it takes to reach the top of its trajectory will be 3 seconds. (b) Show that it will reach a height of 45m (neglecting air resistance). 2. Relevant equations Earth's gravity = 9.8 meter/second² (Professor said to just round it to 10). Equation unknown. d=1/2(g)t² ? 3. The attempt at a solution (a) Played around with Subtracting negative -9.8m/s² (is it considered negative since the ball gets thrown up? - Instead of it coming down?). (b) 45m = 1/2(9.8m/s²)t² - I figure I need to know "t" before I could solve this.
Consider what the definition is of acceleration. It is the rate of change of velocity. If something starts out at 30 m/s and slows 10 m/s every second, it will reach 0 m/s in how many seconds? Here are some formulas for you: https://www.physicsforums.com/showpost.php?p=905663&postcount=2 These lessons might be helpful: http://www.glenbrook.k12.il.us/gbssci/Phys/Class/vectors/u3l2c.html