EJSS 2 Cannon aim at each other Projectile Motion Model m=1kg, g=-9.81m/s^2

EJSS 2 Cannon aim at each other Projectile Motion Model m=1kg, g=-9.81m/s^2

Simulation embedded
sound file taken from http://www.freesfx.co.uk/sfx/bouncing
referencing from http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=144.0
based on a eariler model i made http://weelookang.blogspot.sg/2014/09/ejss-projectile-customized-after.html

Question: do you know why the cannonball always hit each other provided they point at each other and velocities are pointed towards each other and greater than zero?

is conceptually in the green line being without the effects of gravity, the cannons ball will meet as predicted by Newton's 1st Law of motion without net external force.
now, adding the same gravitational acceleration means both cannon balls will move down at the same rate ( pink lines).
therefore, the 2 cannon balls has to collide .

.

 http://weelookang.blogspot.sg/2015/02/ejss-2-cannon-aim-at-each-other.html the beginning run: https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejss_model_projectile2cannon/projectile2cannon_Simulation.xhtml offline: https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejss_model_projectile2cannon.zip scr: https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejss_src_projectile2cannon.zip author: lookang, Fu-Kwun Hwang author EJSS 5.0: Francisco Esquembre
 do you know why the cannonball always hit each other provided they point at each other and velocities are pointed towards each other and greater than zero? author: lookang, Fu-Kwun Hwang author EJSS 5.0: Francisco Esquembre
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