Originally Posted by
MikeSnow
Wait, what? Speed is relative. As a result, kinetic energy is relative as well. Let's say you are sitting down in a train moving at a constant speed of 100 km/h relative to the ground, in a straight line. You as a passenger would have zero kinetic energy relative to the train frame of reference. And if the train wouldn't have any windows (and assuming you can't rely on noise either), you wouldn't even be able to tell if the train is stationary or is moving.
....
Of course.
When you (with mass m) jump off the train with speed v-train, you are going to dissipate: 0.5*m*(v-train)^2.
When you run on the train, with v-run, and subsequently jump off, you are going to dissipate: 0.5*m*(v-train+v-run)^2 (and not 0.5*m*(v-train)^2 + 0.5*m*(v-run)^2).
When you run on the train, backwards, where v-run= - v-train and jump off, you are going to dissipate: 0.
So, debunked (and I leave out the rest of your reasoning, since that qualifies for the same).