Math Problem

[Dunzo]

Anyone know the answer and how to show the work? A quick reply would be helpful

FREIGHT TRAINS

A freight train that is 1 mile long is traveling at 60 mph. A second train that is 2 miles long is traveling at 40 mph. The trains are moving in opposite directions on parallel tracks. How many seconds does it take between the time their locomotives meet and the time their cabooses fully pass each other?

[HavokD]

Oh crap man I forgot about your PM :S Sorry, I saw it and I was very busy at that moment and wanted to give your problem a try later, but I simply forgot about it X.x

Let me give it some thought and once again sorry man :S

[Dunzo]

lol its okay its due tomorrow though soo :x

[HavokD]

I think I got it, are you still here?? I need to put it in some nderstandable text since I made a shitty drawing lol

Ok I will write it fast in here, hope you undrstand me:

First of all, since they travel in opposite directions, we can sum their velocities. If you make both trains "touch" each fronts, and mark that spot with a point, that point will be moving at 40+60 mph= 100 mph.

Now immagine our trains this way, the smaller is 1 mile long, the bigger one 2 miles long. The scale used on the next drawing is |==========| --> This is one mile, ok?

1 mile train up, 2 mile train down:

B|==========|A...........................
........................C|==========|==========|D

Ignore the points, think of them as the tracks of the trains. Now as you can see, A is the front of the 1 mile long train, and C is the front of the 2 mile long train. As we can see, A has to travel up to D+1 mile so the cabooses D and B are side to side, so A must travel 2+1 miles (2 miles to cover the distance of the second train, and one extra mile to get B aside with D.

Now we got everything we need. Velocity is as follows:

v= d/t, and we got out velocity, which is 100 miles, and our distance, with is 3 miles. Just do the math and you will get that

t= 0.03 hours, which is t= 108 seconds.

If someone sees a mistake please tell me asap!

[Dunzo]

thanks so much you're the best! (:

[Farsa]

Equationing the movement for a constant movement object : x=x0+v*t
We are interested in the movement of the points B and D(as HavokD) called them, so we equationate the movements as:
B - xb=-1+60t
D - xd=2-40t
making xb=xd we can solve the problem for the instant they meet
-1+60t=2-40t
t=3/100=0.003s as expected

HavokD's approach is a nice one that makes use of a different velocity reference, against the usual one we have(Earth, vref=0)

[HavokD]

Your answer is much more elegant than mine Farsa xD I hope dunzo sees it on time

[dave88]

What is the purpose of this assignment?

dave,

[tracy]

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