If it's a short, sustained blast that had enough force to knock the man back that hard, then it would probably knock the door back as hard as it did. The problem is, it seems the door just stops. Now I suppose that could have something to do with the man's hand being on the door as he's being shot by the cannon, but I doubt that would have much of an effect without swinging the man off to the left (if he held on very long). Since the man is shot straight back and the door is only slightly in the way of the blast, it would probably be moving after the man flies back. The only forces acting on the door are the cannon, the man's arm pulling on it for however long he might have held on (again, seems he let go right after getting hit), friction, and perhaps the restitution if it were to hit a wall or doorstop. It doesn't seem to hit the wall or anything, so let's narrow it down to friction and the blast. Based on the speed at which the door initially moves after the blast and the average friction of a door's hinge, that door would have to have REALLY sticky hinges to do what it did.Considering he opens the door with relative ease, I doubt it. At the very end of the gif, it would have at least been slowly closing and would have bounced off of the wall; it would not have just stopped after moving about a foot or so, given the full force of the cannon literally launched a 150 to 200 pound (presumably) man at that speed. Now, if you can explain any other variables I'm not taking into play here that would make it do this then perhaps I'll believe it, but this seriously seems like a gag video or something. Funny as all hell though.