BF2S Forums Homework Help Thread

Uzique wrote:

my point was that maths/sciences operate on right/wrong - black n white axis. you know it, or you dont. you get high marks and ace a test, or you fail.

Pure mathematics, yes.  Sciences, no.

Also, 'knowing what you're talking about' because you took high school math?

Bevo wrote:

nukchebi0 wrote:

Looking forward to it.

Integrate force for the change in potential energy, set it equal to the KE at 2.8m :\

fail.

So basically, int(F) - > W -> delta K, so K₀+delta K = K_2.8, and you solve that for velocity?

I wasn't in the condition to think like that when I was helping you yesterday.

Uzique, doesn't the presence of concrete wrong and right answers make the subject harder, especially when being evaluated in an academic setting. It's much easier to fail a test than it is to not get a passing grade on a paper, at least in my experience here.

Last edited by nukchebi0 (2010-03-05 13:37:05)

Electricity and magnetism makes kinematics look easy.

Uzique wrote:

Winston_Churchill wrote:

Uzique wrote:

my point was that maths/sciences operate on right/wrong - black n white axis. you know it, or you dont. you get high marks and ace a test, or you fail.

Pure mathematics, yes.  Sciences, no.

Also, 'knowing what you're talking about' because you took high school math?

higher than high-school level... douche

and yes, i know there are grey areas in theoretical and abstract maths/physics, but nobody here is trying to solve the modularity conjecture's of elliptic curves, are they? it's right, or it's wrong... do your formula... get the proper answer. and no nuk, i didnt find that harder, i found that much easier- because, ironically as churchill said, it's actually much more textbook based...

wow, resorting to childrens insults twice now? Oh so mature and clearly proves you're more intelligent than anyone in math/science

Advanced electricity and magnetism is anything but easy. Or textbook based.  Ever tried something with alternating currents?  After high school math you rarely just plug numbers into a formula, it needs multiple diagrams and a high level of interpretation and understanding of what is happening in the problem to solve it.  Textbooks cant help you with that.

sure thing mr high and mighty.

ill be the mature one and end this so it can get back on topic

okay i need help here.

question is . Show the differential equation

Mdx + Ndy  = 0

will have an integrating factor u(xy) <------ (think that's a typo)

iff

(I think there's another typo there too)

I have not the foggiest clue what this question is asking me. I can work out normal integrating factors ok but this has me lost.

Last edited by Spark (2010-03-07 22:28:39)

yeah, that's what i'm thinking but then it should be f(x,y) not f(xy) because that implies strange things

Spark wrote:

okay i need help here.

question is . Show the differential equation

Mdx + Ndy  = 0

will have an integrating factor u(xy) <------ (think that's a typo)

iff

http://latex.codecogs.com/gif.latex?\bg … \text{xy}) (I think there's another typo there too)

I have not the foggiest clue what this question is asking me. I can work out normal integrating factors ok but this has me lost.

ahhhahaha I have a test in this stuff that's going to rape me in two days

I am really confused about the notation in the denominator though, is that just y times M and x times M? What is the function F? Is that supposed to be a u?

At least when we did it (and the scope of our book) only has integrating factors in either x or y, not both as it looks like that equation implies...

At the most basic level you're looking for u so that (uM)_y = (uM)_x

friggin diff eq....

I am pretty sure that is just out of the scope of my class/book...we would have a problem that would be exactly that without the dx for example. Something like M + Ny' = 0 are the exact equations we're doing...

Spark man, does this help at all?



He was my lecturer for 2nd year Engineering Maths. The champ has put a lot of videos on youtube, under UNSW's "UNSWelearning" youtube channel. he does a question of a similar form to your "(x² + xy + 1)dy + (y² + xy + 1)dx = 0."

mcminty wrote:

Spark man, does this help at all?

http://www.youtube.com/watch?v=rJFVmCgFh6U

He was my lecturer for 2nd year Engineering Maths. The champ has put a lot of videos on youtube, under UNSW's "UNSWelearning" youtube channel. he does a question of a similar form to your "(x² + xy + 1)dy + (y² + xy + 1)dx = 0."

Well I managed to get it out anyway, but cheers regardless.

Hint to FM: The key is to remember that the equation is presumably not in 'exact' form so you have to make it exact, i.e. introduce a u such that (uM)_y = (uN)_x

Last edited by Spark (2010-03-11 04:29:52)

Flaming_Maniac wrote:

Yeah I know, we did integrating factors to make equations exact, but those integrating factors were by definition either functions of x or y. Not both.

well to be honest it was exactly the same. you just had to be more careful when you partially differentiated.

the reason you did u(xy) was that u(x,y) which is the "proper" way to do it for such a general DE but that's just way too fucking hard, so you do u(x), u(y) or something like that instead.

minty, did you try the problem? i got an answer which almost seems too straightforward for the second part of the question (the "hence solve (x² + xy + 1)dy + (y² + xy + 1)dx = 0" bit) - i got u(xy) = e^xy and the solution which i'll call G = e^xy(x+y) + c for any constant c. i mean, it seems to work... but surely it's not that simple?

Last edited by Spark (2010-03-11 04:32:54)

nukchebi0 wrote:

A 10.0 gram piece of Styrofoam carries a net charge of -.700 micro-Coulombs and floats above the center of a large horizontal sheet of plastic that has a uniform charge density on its surface. What is the charge per unit area on the plastic sheet?

I should be able to answer this solely using Gauss's Law, at least according to the placement in my physics textbook, but I fail to understand how I can determine surface charge density without knowing the surface area of the styrofoam, form of the styrofoam, or at least the distance between the styrofoam and the plastic sheet. Am I missing something obvious?

Baffled me, could it be something to do with the fact its made of styrofoam, a specific property of that?