Hi, Im slightly confused by the projectiles colliding question. It say top stone projected at an angle alpha below horizontal, in your diagram it looks like you have alpha as the angle to the vertical. I got horizontal speed of stone to be 20cos(alpha) and cos(alpha) as 3/5 and sin(alpha) as 4/5. Did not seem to make a difference thou as the time calculated was still 2.5secs.
Interesting, yeah I've set that up wrong then. I guess it doesn't matter because there's no reason calling an angle a different thing would lead to a different answer.
