# "One of the girls was thrown hundreds of yards by the impact of the train."

Not true. Sam Stone’s nailed the basic concept, assuming this were a perfectly elastic collision. This equation illustrates it:

m[sub]1[/sub]v[sub]1i[/sub] + m[sub]2[/sub]v[sub]2i[/sub] = m[sub]1[/sub]v[sub]1f[/sub] + m[sub]2[/sub]v[sub]2f[/sub]

Of course it’s a very long way from being a perfectly elastic collision, and the deflections of the train and the persons body would render any mathmatical analysis moot.

My blinding 60-70 mph golf swing (hold the applause) propels a golf ball about 160-170 yards right straight down the fairway. That collision is a lot more elastic than that between a train and a body. If the body was really several hunderd yards from the point of collision then it was carried there by the train for much of the distance.

Nice conspiracy theory, with only a few pitfalls First, putting in an extra ticket machine only provides for those people crossing the railway for that purpose only, and not for those walking along the road. It also only provides for those people wanting a ticket actually provided by the machine. And, if the profit-making companies were so safety-concious, why hadn’t they put a machine in during their tenure?

What a completely useless comparison!

I would appreciate a little instruction from you in this area if you have the time, please sir. My email address is in the profile so that you won’t have to defile the thread with kindergarten stuff.

I don’t see how she could have been thrown whatsoever had the train carried her. If you are being carried by the train, you are moving at the speed of the train. If you are moving at speed of the train you would need a faster train to then come along and hit you so you could then be thrown. So either she was dragged the distance or she was thrown the distance.

If the golf ball is 45g, and the mass driving it (club + torso) is 50kg, the ratio is 1000:1. A three-car Class 170 weighs 130 tonnes, and a 14-year-old perhaps 50kg. A ratio of around 3000:1. Plus, the two different collisions are completely different in many other ways, making any quantitative comparison useless.

In the first stage of the impact, the body has to be carried by the train. Both the front of the train and the body absorb the force of the impact, which then propels the smaller mass (the body) away at a higher velocity. So yes, it’s perfectly possible for the body to be carried part of the way and then ejected forward.

people in these sort of incidents are often dismembered, thus complicating your calculations. A police officer friend of mine who has attended all too many of these incidents recalled finding a complete face, detached from the head.

Sam, my impression is that you have a pretty good history of posting factually correct things here at the SDMB, but I have to call BS on this one. If this were a perfectly elastic collision, it should be possible to use the train’s change in speed to calculate the body’s change in speed with conservation of energy techniques.

But this is not an elastic collision - I would wager that it’s close to being perfectly inelastic. The body would be left with a max speed of that of the train itself, but be pushed off to the side and would tumble to a stop. I can’t believe that a body would bounce off the front of a train at all.

I’m pretty sure that based off various videos I’ve seen of these accidents it’s a partially elastic collision. Still, with the varied terrain (body rolling downhill, etc.) the uncertainly of the angle of incidence (to both the Y and Z axes) and the amount of energy absorbed by the two bodies it’s totally pointless to try and debate the math involved.

I was not intending to speak in absolutes - I recognize that in order to be thrown there must be impact and that it will last for some measurable time. But David Simmons said, "* If the body was really several hunderd yards from the point of collision then it was carried there by the train for much of the distance.*

A train travelling 90mph requires 2.29 seconds to traverse 51% of 200 yards. I can’t do the physical mathematics but I have a good hunch that she was not in contact with the train for nearly that long…

In an earlier post, I’ve already suggested that even if she were thrown forward, she would still be carried by the train for some of the distance, and I went for one second. I also observed that journalistic-licence ‘hundreds of yards’ could actually mean one hundred yards.

I think one second is too long. It equates to the two being in contact over 132 feet. How could we calculate the length of time the two were touching?

In the article you linked 200 was the lower limit. “One of the girls’ bodies was found fairly close to the station. The other had been thrown 200 to 300 yards up the track."

What’s the problem with that?

We can’t.

It’s the same quote as that in the OP, except one or the other has been paraphrased by a reporter. So 200 is no more accurate as a working figure than 100.

The quote in the OP is a quote of a paraphrase, thus it is a quote of content of the article and not of the actual words that a person said. The quote of the words that an actual person said are that the distance is between 200 - 300 yards. Even we were sticking to your pedantism, 100 does not qualify as “hundreds” of yards.

I’ve been reading physics papers, and while I haven’t found a formula I can use, I see that physicists frequently use duration of contact when doing calculations concerning bodies in contact. If you don’t know how that’s fine…but I don’t understand the nonsense about the distance.

That’s missing the point of how journalists can use quotes. The interview could have gone as folllows:

Ambulance service: “The body was thrown some distance”

Interviewer: “Specifically how far was it thrown? Hundreds of feet?”

Ambulance service: “Yes”
The reporters are then at liberty to report as in the OP, and this can then be paraphrased in the way my linked article did. In short, you can’t rely on such figures as being in any way accurate.

I’m sure they do, but without knowing very much about which part of the train hit her, and the exact properties of that part of the object, we can’t do this with any accuracy.

You’re right that you can’t be accurate about this, but you can say with certainty that if the body traveled with the train for longer than .25 seconds it would be a completely inelastic collision and totally render your point moot. The time in which the body would have travelled with the train would be a very small portion of the target distance.

Beyond that I’m at a loss to gather what your point is at this stage. Debating the physics of the impact and trying to extrapolate a distance knowing just the speed and weight of the objects is so pointless in light of all the unknown quantities and the dubious reporting that you might as well be trying to calculate the color of her panties.

The term “thrown” was the descriptive used by the reporter who wasn’t there. We have no idea from the news story whether the body was thrown. pushed, dragged or any other combination of methods.

[quote=GorillaMan} If the golf ball is 45g, and the mass driving it (club + torso) is 50kg, the ratio is 1000:1. A three-car Class 170 weighs 130 tonnes, and a 14-year-old perhaps 50kg. A ratio of around 3000:1. Plus, the two different collisions are completely different in many other ways, making any quantitative comparison useless.[/quote]
Any quantitative calculation for this problem is meaningless anyway. Me post was merely illustrative as are all of the others in the thread.
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Sorry to brake it to ya, but it is true when the mass of one object is very large to that of the other (technically it approaches 2x). It is the same of bouncing a superball against a wall, the superballs velocity is the same but in the opposite direction.

Ball moving at the wall at 70mpg, leaving at -70mph is the same as the ball at 0 mpg, wall at -70mph, and after the ball will be moving at -140mph.

I remember in High School we had a disabled woman come in for a lecture and tell us that she was on the back of a motorcycle that was in a collision and she was thrown 300 yards. It took a great deal of self-control for me not to ask her if she was on the moon at the time.