1. The problem statement, all variables and given/known data A shell is shot with initial velocity v0 of 20 m/s at an angle 60 degrees. At the top of the trajectory, the shell explodes into two fragments of equal mass. One fragment has a speed of zero immediately after the explosion and falls vertically. How far from the gun does the other fragment land, assuming terrain is level and there is no air drag? 2. Relevant equations i don't know! 3. The attempt at a solution i have no idea. i want to use v1f = (m1 – m2) / (m1+ m2) * v1i, but that leads to v1f = 0 which is clearly not correct in this situation -- why not? and if i use and v2f = 2m1 / (m1+ m2) * v1i, then i just get v2f = v1i, which is clearly not correct either. or maybe these are correct, like v1f is the fragment that falls vertically, and v2f just equals v1i somehow. but i still can't figure out how to get any distances out of this. i really hate this problem, having looked at it for way too long, and i think my teacher will use something like this on the exam because he covered it again yesterday in class. this is what he wrote on the board: vf = (m1+m2)/m2 * v0cos60 r - r0 = vft - 0.5gt^2 = Di - Hj D = vft -H = -0.5gt^2 D = vf sqrt(2H/g) i'm sorry but this makes absolutely no sense to me. i vaguely recognize some of the projectile stuff here, but there's no way i could have done this on my own. in fact, i can't even do it with these notes in front of me. please help me. any advice on how to break this down. thanks.