1. The problem statement, all variables and given/known data The speed of a projectile when it reaches its maximum height is one-half its speed when it is at half its maximum height. What is the initial projection angle of the projectile? 2. The attempt at a solution First I tried to find the speed for the max height. vf2 - vi2 = -2gΔd vf2 = vi2- 2gΔd 0= vi2- 2gΔd <--- Can someone explain why this must be set to zero? ∴ vi=√(2gh) After that I did the same for half the height vf2 - vi2 = -2g(Δd/2) vf2 = vi2 - g(Δd/2) 0= vi2 - g(Δd/2) ∴ vi2=√(gh) After reaching this point I'm not really sure how the given information can help give me an angle. I know somehow I'm supposed to break it down into horizontal components but I just can't see it. Any help would be appreciated.