Let's say we have two cannons aimed directly at one another ( as my horrible attempt shown in the image ).
The Angles The cannon on top is aiming down towards the one on bottom right, and of course, the bottom one pointed upwards. They are pointed towards each other as exactly as can be.
Resistance It happens to be the calmest day in recorded history. There is no air resistance at all.
Coordinated Shots Let's assume both cannons are fired at the exact same time, exact same speed and power. Yes, aimed at each other.
What will happen?
Note: Before considering tagging this puzzle "too vague", or "not enough information provided", which is at first-glance a reasonable assumption - I just want to assure you that there is a consistent outcome.
Hint: Read up on this topic if you get stuck:
fixed-point theorem in topology
Good Luck. I'm looking forward to seeing some work written out. I have the answer fully documented when it's time to post it.