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If you download the video, the frame rate was 30fps and it took the piece of metal 12 frames to reach the cameraman (or camerawoman) so that was so that was a total time of 0.4s to travel a distance equivalent to ~25 steps (the amount of steps that the woman ran after lighting it up). Assuming that each step was ~1m, that would be equal to roughly 25m.
Avg. Velocity = Δdistance/Δtime = 25m/0.4s = 62.5m/s
Assuming that the piece was made of a stainless steel alloy (like this microwave part) with a density of 7,750kg/m3 with dimensions of 0.4mm (0.0004m) x ~0.5m x ~0.25m; the mass of the piece was the following:
Mass = (volume)(density) = (0.0004m)(0.20m)(0.4m)(7,750kg/m3)=0.248kg
The Avg. momentum that the piece had was then: p=massAvg. velocity=(0.248kg)(62.5m/s)=15.5kg*m/s
If we assume that the object stopped completely, the change in momentum would equal the Avg. momentum minus zero (final momentum). Newton's 2nd Law (F=m*a) is really just the change in momentum with respect to time (what appears to be ~2 frames in the video), so we get that the force exerted on the person by the object was:
F=Δp/Δt=(15.5kgm/s)/(2frames/30fps)=232.5N (roughly 52 pounds of force*)
Depending on the angle at which it impacted the person, it could have caused significant damage (if it impacted on the sharper edge, with less surface area to decrease the force/area (stress) that the body part would have been subjected to. In the video it seems as if he got lucky and was hit with the larger area side.


