Math Problem!!!!
 

A train is running at the speed 40 m/s , suddenly the driver pushes the brake and it reduces to -2 m/s^2 .

Question : After 30 seconds, how far can that train go ?


:Graucho

400meters because it would have stopped @ 20 seconds

about 100 miles. yeah, yeah definitely about 100 miles.

scientific answer please. no guessing!!! :Graucho :glugglug

400 how ?

100 how ???

I made this image a long time ago for another one of Luc's threads but I didn't get around to posting it. This is probably as close as I will ever get to having another chance, so here it is :)

<IMG SRC="http://friends.porncherry.com/images/original/aznmath.gif">

SpaceAce

40 m/sec, slowing down @ 2m/sec makes it 20 secs before it reaches zero.

the graph forms a rectangle triangle with 1 side measuring 40, and the other measuring 20, to find the surface of the triangle, wich represents the distance in meters, you do (40 X 20)/2 wich gives you 400 meters.

didnt you learn anything in physics class?

damm metrics... how many MPH is that??

you're very tricky!!!:warning

d=.5(a×t^2)
d=.5(-2m/s^2×30s^2)

The train will travel -900m. :eyecrazy

m/s = meter per second.

fuck no
m/s = meters per second

what kind of thing could go @ 40MILES a second?!?!?!

The liquor store is 12 km from my house, and it closes at 11 pm. If I drive at 70 km/h all the way there, buy a 66'er of vodka on sale for $38.95, then drive at 60km/h all the way back, can I feasibly be drunk by midnight?


No using a calculator!

the answer is definately yes

ok:1orglaugh

read the problem carefully.

40 meter per second reduces to minus 2 meter per second square (-2 m/s^2)

It's slowing down by 2 meters per second squared, not 2 m/s.

Edit: Luc beat me to it.

But having a right answer simply isn't good enough on this thread. Please illustrate the scientific formula you used to arrive at that conclusion. Please illustrate all calculations, trigonometry, calculous and vectors used.

need help with your HS math hw luc?

meters per second squared is the general writing for of acceleration, but its slowing down @ 2 meters per second, only because its acceleration we put it squared, cuz thats how it is

ask a scientist, hell give you the same answer as me

800+

here, I made a pic for you
http://www.wantsmut.com/luc.JPG

Yes, yes I see now that you are right by your calculations. I absolutely CAN be drunk by midnight.


thanks :D

no problem buddy, enjoy! :thumbsup

Ok, time to school.

x= x(not) + v(not)t + .5 at^2
x(not) = 0
v(not)= 40
t = 30
a = -2
t = 30

300 meters.

your calculations show that the train would be going backwards from seconds 20(excluded) to seconds 30(included)
we both know that this cannot be true if the person uses the BRAKES :thumbsup

a^2+b^2=c^2

Area of that triangle does not = a+b/2

what you are showing me is Pythagorus, that is to find the lenght of the segments...
the triangle area is represented by (A *TIMES* B)/2

:thumbsup

No, it would have stopped based on the problem. Of course it's not going backwards.

Hell yeah, you probably left at 2pm you fuckin' alco :1orglaugh :1orglaugh
:glugglug

thats why you need a graph,

u got owned buddy, u got owned :1orglaugh

Yes, you're trying to find the length of the side, ie, the length of the train ride, not the area inside the triangle.

lol
what does the lenght of that side represent?
we are trying to find the surface, wich represents the position in meters, compared to the initial position, wich is 0

Dude, distance is not equaled by the surface area. Where did you learn that? Distance is equaled by the side of the hypotenuse (sp)which is why you would use the Pythagorium (sp) theorm.

revise brudda, I studied in this, I know it like the back of my hand :thumbsup

Im honestly willing to bet any amount of money on this :thumbsup

BRING IT ON BITCHES :Graucho

Ok, let's work on this here. You graph is showing that 2m/s is the hypotenuse, when it's actually supposed to be on the X access. The hypotenuse is the distance, which you are trying to find. Agree or disagree?

its not the hypotenuse, its the "pente", as we say it in french....
whats the word for english, ARGH

its Y/X, I dont know what the english word is for it

the slope I guess? (I just checked a french english dictionnary)

The slope is the hypotenuse. Your graph is showing time as the distance. The 2 m/s should be on the x aixs, not as the slope. That's what you're trying to find.

the graph is speed in the function of time

the vertical bar represents the speed in m/s
the horizontal bar represents the time in seconds
the diagonal represents the slope, wich represents the acceleration (-2m/s^2)
and the surface of the triangle represents the distance traveled

Physics that uses numbers and calculations is gay. True Physics is all theory.

Mr.Wrong
here you go

http://www.physicsclassroom.com/Class/1DKin/U1L4e.html

please read it carefully, it shows that the way I calculated is the correct way

:thumbsup

actually it got negative decellaration
so it should go backwards

not in this context, because after a full brake, the train wont go backwards, it will just stop moving

30 times farther then it was 30 seconds ago

I found interesting in BDJUF.

BDJUF, you just got yourself rekon by your greatness.

:thumbsup

Mr. Wong. You're full of knowledge too!!! :thumbsup

Didn't even see this. This is also correct. The train will travel -900m. How long would the train travel total? 1200 miles.

What's 1200-900=300 meters.


bdjuf where do you even address the time 30 seconds in your equation?

i'm coming up with 900 meters and here's why, instead of using vector analysis i used D= 1/2*(A*T^2)
D is the distance you're looking for, a is the absolute value of your acceleration and T is the time (30 seconds)

it's the same formula you use to calculate how fast something will fall with gravity except you replace the A with the gravitational constant.

that makes any sense or am i just high?

wow i was so fucking late on that. :Graucho

omg, i knew this stuff at 9th or 10th grade or something..

how many of you are high school dropouts?