Physics--so hot right now (another question)

C

Cooldude

Member
Ok so since it seems like the cool thing to do, I decided to post yet another physics question:

You are standing in a field by a train track, because thats what you like to do. Then a train of length L comes flying, and i mean flying (well not really, rolling, but quickly) down the track at 4c/5 (4/5ths the speed of light). The question is:

You wanna time how long it will take for the train to pass you. What do you conclude?

[hint* How long is the train?]
 
Its a totally legit question lat. And mk2 you are on the right track (get it train track, haha!) but i was actually looking for like a duration of time for it to pass, sorry if that wasn't clear.
 
i dont really see how a train travelling 80% the speed of light is legit. its impossible. maybe in another 2000 years but in our life time......never
 
Distinction:

I claimed the question, not the circumstances or actual feasability of the damn thing, is legit. It is a very basic analogy used to describe behaviors of natural phenomenon that actually do occur on this scale (thats another clue for y'all).

As for an actual train moving at that speed, i agree, that is rather difficult/unlikely...so lat, you can have a cookie, too.
 
Are we talking about time relative to the train or relative to the person watching the train go by ? Which would be respecitivly different - so long as the speed of light is defined by the speed of two protons moving in opposite directions
 
I got my physics test on power back, (I'm in AP Physics) yea, I fucked up. lol, 20/50 he had to curve the whole class, so I ended up with a 70, lol, 30 point curve. And I suck at physics, I have a 73 in there. It sucks.
 
i do understand what you are trying to say and i give you that also. so now were on the same boat we can share cookies
 
Length Dilation (contraction) property of relativity. So do you want the actual length, or the length that it appears to be?
 
and by cookies lat means loads.

you need to know the length of the train if you want an actual time
 
this could be the dumbest post ever... not because the problem is idiotic (which it is), but because you called it physics instead of MATH, which it is
 
i took physics at the beginning of the year but then i had a 30% for the first quarter so i got switched to earth science
 
nobody likes the class at school, please keep these question to yourself. I have tried to get answer on here before to and i had no such luck.
 
since distance = velocity * time, then time equals distance/velocity so then put 2 and to together and you come up with

(L/(4c/5))

that is from the observer in the field. as for on the train, fuck that i have no idea.
 
I conclude that you would be killed by all the flying debri that a train going at almost the speed of light would be dragging
 
Alright here's the answer:

A couple of you guys got really close though not quite, others were just mean, and hurt my feelings!!! Anywho:

The train is length L, but as it is traveling so fast, it is actually shorter than L. In fact it is shorter by a factor of gamma, which in this case is 5/3. The actual train length is (3/5)L and so the time it takes is only (3/5)L/(4/5)C = 3L/4C

Now im sure you all can sleep at night
 
i thought it would only 'appear' to be shorter to the person who was standing still but would not actually be a shorter train ? Kind of how it's mass increases relative to itself but its not actually gaining any mass ..i pooped a hammer
 
the turbulence in the air from the damned thing would turn your ass inside out before you knew the shit had got to you man
 
the crazy thing, is the train is actually shorter. The whole thing about relitivity, is precisely that, its relitive and depends on your perspective, there is now "proper universal frame". But how can it be both L and a shorter fraction of L you ask? Well its not, simultaneously. Its a little bit similar to having two people stand a little ways away. There is nothing wrong with person A saying, I am bigger than person B, and at the same time person B saying, im bigger than person A. Totally dependent on the point of view.
 
You must log in or register to reply here.
Back
Top