Iron Edge

Iron Edge => General Discussion => Topic started by: Archz on May 18, 2009, 06:26:28 pm

Title: Math geeks, assemble!
Post by: Archz on May 18, 2009, 06:26:28 pm: So, theres a math problem that is haunting me:

d)

"(...) after 5 second a parachutist releases his parachute. We assume that the air resistance (drag) will now become -k * v(t)^2. We set g = 10 and k = 8."

"Use Newtons 2. law to set up a differential equation for the situation when the parachute opens."

(The guy weighs 80 kg)

ma = mg - L

ma = mg - (kv^2)

v'(t) + k/m * v^2 = g

v'(t) + 0.1v(t)^2 = 10

So far so good I think

but then:

e) "The differential equation in d) is separable. Set v instead of v(t). Show that we can write the differential as: (attachment)"

f) "Find an expression for v by solving the differential equation in e)"
Title: Re: Math geeks, assemble!
Post by: Grishnag on May 18, 2009, 06:31:45 pm: EEEEEEEEEEEEWWWWWWWWWWWWWWHHHHHHHHHH math
Title: Re: Math geeks, assemble!
Post by: Archz on May 18, 2009, 06:37:50 pm: Thank you Grish :p

I was well aware that my chances were slim, but I've had help from the guild before!

Come on, halp plox!
Title: Re: Math geeks, assemble!
Post by: Palmar on May 18, 2009, 06:55:16 pm: I'll look at it, though my physics are a bit rusty...

But can you please photograph/scan the entire thing so it's not horribly set up?
Title: Re: Math geeks, assemble!
Post by: Archz on May 18, 2009, 07:03:59 pm: It's in Norwegian :p

The first thingie is the calculations that I have made, if you grap some paper and write down the last differential that is underlined, it might be easier.
Title: Re: Math geeks, assemble!
Post by: kagemoth on May 18, 2009, 07:20:29 pm: (http://img95.imageshack.us/img95/3659/16822586.jpg) (http://img95.imageshack.us/my.php?image=16822586.jpg)
Title: Re: Math geeks, assemble!
Post by: Starbrow on May 18, 2009, 08:05:44 pm: I'd love to help, although I'd like to see the paper, instead of your attempt at explaining, even if it's norwegian...
Title: Re: Math geeks, assemble!
Post by: Palmar on May 18, 2009, 09:36:31 pm: best part is, he didn't even define the variables :)

For your own good, shape up on format!

And yes, let us see the paper, even if it's in norwegian.
Title: Re: Math geeks, assemble!
Post by: Archz on May 18, 2009, 09:46:39 pm: http://www.ulven.biz/r2/eksamen/r2_eksempel.pdf

Sorry, thought the variables kinda explained themselves ^^
Title: Re: Math geeks, assemble!
Post by: Supremacy on May 19, 2009, 12:00:52 am: OMG NOOOO MATH!!!! IT FOLLOWED ME EVEN HERE!
Title: Re: Math geeks, assemble!
Post by: Goza on May 19, 2009, 10:02:12 am: (http://icanhascheezburger.files.wordpress.com/2009/02/funny-pictures-your-cat-is-confused-by-algebra.jpg)
Title: Re: Math geeks, assemble!
Post by: Daekesh on May 19, 2009, 01:27:42 pm: Is that Shiftey?!
Title: Re: Math geeks, assemble!
Post by: Supremacy on May 19, 2009, 02:05:36 pm: Quote from: TTaM on May 19, 2009, 01:27:42 pm
Is that Shiftey?!

Must be!
Title: Re: Math geeks, assemble!
Post by: Archz on May 19, 2009, 04:07:38 pm: Come on guys, exam tomorrow!

Starbrow, Palmar, Tyler! Braintrust gooo!
Title: Re: Math geeks, assemble!
Post by: Shiftey on May 19, 2009, 04:36:35 pm: (http://ihasahotdog.files.wordpress.com/2009/02/cute-puppy-pictures-elebenty-hotdogs.jpg)
Title: Re: Math geeks, assemble!
Post by: Goza on May 19, 2009, 04:44:21 pm: (http://i41.tinypic.com/m37rd.gif)
Title: Re: Math geeks, assemble! TYLER HELP PLOX!
Post by: Archz on May 19, 2009, 08:29:08 pm: Tyler! Help me please!
Title: Re: Math geeks, assemble!
Post by: Fatalbone on May 20, 2009, 02:02:53 am: there is no tyler here... only fatalbone.(solved by my engineer friend)

d)you made a mistake missing a - or - minus in equation
e)solveable now but ugly algebra
dv/dt+0.1-v^2=10-->dv/dt=10^2/10-v^2/10
dv/((10^2-v^29/10)=dt-->(10/((10-v)(10+v))(dv/dt)=1 you can find from there looking to answer.

f)(1/(10-v)+1/(10+v))dv=2dt--> integral(1/(10-v))dv+int(1/(10+v))dv=int(2)dt

-ln(10-v)+ln(10+v)=2t

ln((10+v)/(10-v))=2t

e^ln((10+v)/(10-v))=e^2t

(10+v)/(10-v)=e^2t

you should be able to solve from here even I managed to solve f. These questions are easy differentials but very ugly algebra.

you should get v=(10e^2t-10)/(1+e^2t)
Title: Re: Math geeks, assemble!
Post by: Goza on May 20, 2009, 10:07:27 am: Moonspeak.
Title: Re: Math geeks, assemble!
Post by: Kendoki on May 20, 2009, 11:28:16 am: Me r scared of this talk! :o
Title: Re: Math geeks, assemble!
Post by: Smorisha on May 25, 2009, 02:55:40 am: two times nothing equals nothing, worm was never there!
Title: Re: Math geeks, assemble!
Post by: Archz on May 25, 2009, 04:31:40 pm: lul necro!

Wasn't that hard actually, solved it some time ago but I don't have a scanner =(

(looks too messy in computerwriting)
Title: Re: Math geeks, assemble!
Post by: Hisagi on June 03, 2009, 10:23:04 pm: wat languange u naow speak? :o