I saw this video posted on Physics and Physicists:
https://www.youtube.com/w
It reminded me that I had at one point tried to analyze this. I had actually posted something about this on the first generation of my blog (which no longer exists). I have found the analysis, and here it is from the archives. Thanks ZZ for reminding me.
Could this be true, or is it fake? I started to do an analysis of the trajectory, but I found the following frames:
Look at the guy's back. His back starts moving before the water bottle rockets. It must be some type of cable pulling him. If the rockets were propelling him, the rockets would move first.
What about the energy? Is there enough energy stored in these water bottles to get this guy this high? First, how much energy? I know this isn't exactly correct, but the best I could find is that there are 17 Wh per liter of compressed air. (yes, it would depend on the pressure - but let me proceed anyway since I don't even know the pressure anyway). So, how much compressed air?
From this picture, it looks like there are maybe 10 bottles. They look bigger than a 3 liter bottle, so I will guess they are 4 liter bottles (do they make those)? The bottles look like they have maybe 1 liter of water in them. That would give 30 liters of compressed air (probably not more than 60 psi or the bottles might explode). The energy stored in compressed air can be calculated with the following:
110 
kJ/m3 at 25 °C (298 K), per mole. This would give:
Where I assumed the bottles were compressed to 60 psi (about 4 atmospheres) using 6 moles of air. So, now the guy has some energy (even though I made tons of approximations). So, if all this energy just went to increasing the gravitational potential energy of a small Japanese guy, how high would it go?
Wow, that is pretty high. But the water has to also be lifted. Suppose there are 10 liters of water and half of it has to be lifted, that would make this it go 51 meters high. This doesn't seem to be correct, let me move on.
How about I analyze the trajectory of the guy? This is a little difficult because the motion is not at a right angle to the camera, but I will proceed anyway (that's what I do).
Here is a plot of the vertical position (not adjusted for the angle) versus time. I scaled the video assuming the people were about 1.7 meters.
A few things to look at. First, the speed on the way up is about 3.9 m/s. On the way down, I would assume a near free-fall speed. This should be near 9.8 m/s2 but from the quadratic fit, the acceleration on the way down is around 1.4 m/s2. Wait, this is totally messed up. I need to work on my video analysis techniques.
