Example 

"For example, a train that weighs 1 kg moving at 500 m/s and that hits a 'perfect' steel wall where it uniformly decelerates from 500 m/s to 0 m/s in .02 seconds, has an approximate impact force of 25000 N. Thus, a body which decelerates more quickly has a greater effective impact than one which decelerates more slowly."

I'm not doubting the calculation here, but the example is a bit unusual.  500 meters per second is equivalent to about 1118 miles per hour, faster than a bullet train.  And a 1 kg train is like a toy train or something... so in my head I'm imagining a toy train breaking the sound barrier and smashing into a steel wall.  I'm not sure what a typical train weighs (maybe 50,000 kg), but apparently their max speed is about 50 mph or 80 km/h or 22.222 m/s.

50,000 kg * 22 m/s / 0.02s = 55,000,000 N

There. Doesn't that turn into a nice number? 130.184.250.29