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#11 Molly Mae

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Posted 29 September 2011 - 05:03 PM

I'm assuming that the paths of the fly and the train are collinear and each are traveling toward one another.
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#12 guppy

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Posted 29 September 2011 - 05:16 PM

then if that is the case then and there is no turn as mentioned that yh the fact that it would get to a 0 is correct ... if not i blv the answer will change
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#13 guppy

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Posted 29 September 2011 - 05:18 PM

what is up with me today! can't form a sentence without some form of slip up... i handed in an essay 2day...that should go nicely-_-'
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#14 riddlemetodeath

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Posted 19 October 2011 - 10:01 AM

look at it like this...

two cars are nearly going to crash. let's pretend that they didn't use the breaks or the there was ice and they couldn't stop.

If you were in one of these cars, and you looked and you checked the speed at the time of contact, the car wouldn't go any faster/slower until a fraction of a second later when the other car goes flying overhead.

Obviosly, 10km/h
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#15 guppy

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Posted 23 October 2011 - 03:08 PM

i don't think the speed can be 10km at pt of contact.. when the cars hit the speed ofcourse goes down..and u also have to take into account that the fly is much smaller than the train.. the train will be un-effected by it crashing into it so it just keeps going
but the fly at pt of contact as to have decreased in speed or even reached zero... before going in the other direction
i liked a previous analogy of it by maurice.. imagine it as a baseball game..when the ball hits the bat it can't remain at the same speed as it was while flying when it hits the bat it has to decelerate and head in a different direction
and since in this case the fly and train are facing each other in a straight line then when the fly hits the train it will then start heading in the same direction as the train which is 180 it's original direction and for that to happen it must reach ,at a certain pt, tothe velocity 0
so i don't blv it to be at the same velocity at pt pf contact
if anything i think at pt of contact it is zero

Edited by guppy, 23 October 2011 - 03:10 PM.

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#16 Molly Mae

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Posted 24 October 2011 - 04:35 PM

so i don't blv it to be at the same velocity at pt pf contact
if anything i think at pt of contact it is zero

Is the deceleration instantaneous? If not, why would the fly be slowing down before it hits the train? This is the core of the question. I believe the speed to be 0 a tiny fraction of a second after impact (which implies that the momentum of the fly affects the momentum of the train--which it does...but only so slightly).
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#17 guppy

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Posted 26 October 2011 - 06:20 PM

ahahahah that's not really what i meant MM... i think i was trying to be polite by not being too blunt of whtvr... i was tired :P
we discussed this already and we got to 0 and i blv it to be 0 at contact.
.... mmm i see your pt... but is the train really effected .. even slightly?
the fly to the train might as well have been dust in the air to us while we walk...
dust doesn't effect us.... does it?0.0 i know either way it's negligible but does it even effect the momentum at all?
aren't some thing considered null? (although i do find logic in your reasoning and i do agree but i don't think it applies here or does it?)

Edited by guppy, 26 October 2011 - 06:22 PM.

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#18 Molly Mae

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Posted 27 October 2011 - 04:36 PM

ahahahah that's not really what i meant MM... i think i was trying to be polite by not being too blunt of whtvr... i was tired :P
we discussed this already and we got to 0 and i blv it to be 0 at contact.
.... mmm i see your pt... but is the train really effected .. even slightly?
the fly to the train might as well have been dust in the air to us while we walk...
dust doesn't effect us.... does it?0.0 i know either way it's negligible but does it even effect the momentum at all?
aren't some thing considered null? (although i do find logic in your reasoning and i do agree but i don't think it applies here or does it?)

The fly's momentum (mass and velocity) certainly do affect the train, but not on any real measurable scale, so you could count it as negligible for the sake of any other problem, but does exist (since momentum can't be destroyed). The fact that the affect does exist, though, is proof enough that the fly decelerates to 0 after impact.
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#19 guppy

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Posted 29 October 2011 - 06:35 PM

ahhhh well thank you MM that clears things up.. so basically what you are saying that there isn't usually a null factor but rather a negligible factor but the factor still exist no matter the speed or circumstance?
well i can make sense of it and it's logical so that's gd enough for me :P
so the fly reaches 0 at a tinnnnyy microsecond of time after impact with the train would be our final conclusion.
but using that logic u kinda feel weird when thinking that if u are walking and there is like bundles of dust particles in the air or if someone somehow throws droplets of water at you while walking or running, it effects your momentum. i would have never thought about it or assumed that they would :P
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#20 voider

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Posted 02 November 2011 - 06:06 AM

People who have done high school physics will know that collisions are associated with a finite period of time. It is not inappropriate (for general purposes) to model the fly's acceleration as constant during contact.
The fly may end up sticking on the train, or bouncing off it. There are other complications with making use of the provided speeds.
Either way, the "moment" in question is not an instant, so if you took "moment" as "period of time" then the most informative answer might be:
v(t) = (vf - vi)/(Δt) * t + vi, 0 <= t <= Δt
We know vi = 10 kph.
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