So we launched catapults on Friday, that was pretty intense. In theory, ours was utterly perfect. We optimized it mathematically, and built it with the strongest $1.99 2x4s in all the land. What we didn't account for was wind. Not wind's effect on our projectile, but on the catapult itself.
When cocked, our catapult had 135 pounds roughly four feet in the air (about 700 joules of potential energy, for those keeping score). During one launch our catapult, well, fell on me. If it fell two feet before hitting me, it was moving at (super rough mental math) ~1.5m/s.
More interestingly, the piece of rebar I was hit with was half inch diameter, or .00051 square meters. This becomes an average of 690371 Joules/square meter of my flesh. In turn we can convert this measure to Langleys, we see I was hit with the equivalent of 16.51 ly of solar radiation, a dose surely considered hazardous in any reasonable scientific culture.