Oooohhh CRAP Exam in 5 hours, need help with this problem.

[Trevelyan]

Oh man my Calc3 final is in 5 hours and i can't figure out this problem on the practice final.

It's kind of tough, but I keep getting stuck and I think I'm approaching it the wrong way. You will literally be saving my grade if you can help me with this, because chances are he's gonna put something like this on the final.

If anyone can do it, I would be much obliged:

Use Stoke's Theorem to find INT(Fdr) over curve C where C is the curve parametrized by <cost,sint,cost-sint>, 0<t<2pi. And F(x,y,z)=<5yz,x^2-y,yz>.

If anyone can do it, it would definately help a lot. First thing I did was change the parametrization of C to in terms of x,y, and z, but I think that is where I'm going wrong. Then I changed it to an integral over a surface S of curlF, and then to an integral over a region D, but I didn't know what to set the boundaries to, and the boundaries I got gave me zero for an answer.

<REWARD>
If someone can do it I'll send them 2 crisp dollar bills in the mail, oh yes.
</REWARD>

 

[Trevelyan]

Oh, and I most likely will be falling asleep here in about a minute or two ...

 

[Xionide]

49?

 

[Pepsi90919]

Originally posted by: Xionide
49?

42.

 

[Gooose]

42

 

[IAteYourMother]

what ^^ said

 

[Trevelyan]

...................................................................................................................

 

[vshah]

if i'd paid attention in calc 3d i could have helped you. unfortunately i didn't attend the last 3 weeks of classes (which dealt with stokes theorem). still got a B though. sorry. 🙁

 

[BRObedoza]

i just took my final in mathematical physics, surface integrals included.

naturally, it's all gone from my head now.

 

[Aimster]

I have an exam in ...9 hours.. w00t

 

[Darien]

Is that reward still good? Let's see if I remember myc alculus. . .

 

[Ryuson99]

Instead of giving just an answer wouldn't he need an explination?

 

[Schrodinger]

http://www.physicsforums.com if no one here can help you (but hopefully they will)

 

[JohnCU]

Just let x = x, y = y, and z = 0

r(x,y) = <x, y, 0>

Take the partials of r with respect to x, then y, then use those two equations and do a cross product on them.

Then your integral becomes int(0 to 2pi)int(0 to 1) of curl F dotted with (rx X ry) dA

Convert to polar coordinates to finish it off (note I already put the limits of integration in polar form, but like, if you see an x in the equation, it becomes rcos(theta), etc...

 

[Darien]

I get 0 as well. Of course I haven't done this kind of problem in a long time, so I might be wrong

 

[Darien]

Hmm...just realized the op posted more than 5 hours ago. No use in posting my solutions then. GL op :thumbsup:

 

[bleeb]

Originally posted by: JohnCU
Just let x = x, y = y, and z = 0

r(x,y) = <x, y, 0>

Take the partials of r with respect to x, then y, then use those two equations and do a cross product on them.

Then your integral becomes int(0 to 2pi)int(0 to 1) of curl F dotted with (rx X ry) dA

Convert to polar coordinates to finish it off (note I already put the limits of integration in polar form, but like, if you see an x in the equation, it becomes rcos(theta), etc...

 

[GasX]

I used to be an ace at math. I placed out of all collegiate math requirements, etc.... 🙂

I couldn't understand anything in that problem... :Q

Use it or lose it, folks... 🙁

 

[Trevelyan]

Well I'm back from the exam, and unfortunatldy didn't get to read this before taking it... but not too worry all went well and I at least got a B, hopefully an A. Some of the questions were freakin tough! About an hour into it I had 3 problems out of 5 left that I didn't know how to do, but luckily I figured them out (at least I think so 😉) in the last hour.

After doing the problem on the practice exam I got 0 as well. Thanks JohnCU for your reply... PM me your address for some two dollars...

 

[JohnCU]

Originally posted by: Trevelyan
Well I'm back from the exam, and unfortunatldy didn't get to read this before taking it... but not too worry all went well and I at least got a B, hopefully an A. Some of the questions were freakin tough! About an hour into it I had 3 problems out of 5 left that I didn't know how to do, but luckily I figured them out (at least I think so 😉) in the last hour.

After doing the problem on the practice exam I got 0 as well. Thanks JohnCU for your reply... PM me your address for some two dollars...

You mean I told you the right way? woo hoo, keep the two bucks though 😉

 

[chuckywang]

Originally posted by: JohnCU
Just let x = x, y = y, and z = 0

r(x,y) = <x, y, 0>

Take the partials of r with respect to x, then y, then use those two equations and do a cross product on them.

Then your integral becomes int(0 to 2pi)int(0 to 1) of curl F dotted with (rx X ry) dA

Convert to polar coordinates to finish it off (note I already put the limits of integration in polar form, but like, if you see an x in the equation, it becomes rcos(theta), etc...

I have taught you well, grasshopper.

 

[Hankerton]

Originally posted by: chuckywang

Originally posted by: JohnCU
Just let x = x, y = y, and z = 0

r(x,y) = <x, y, 0>

Take the partials of r with respect to x, then y, then use those two equations and do a cross product on them.

Then your integral becomes int(0 to 2pi)int(0 to 1) of curl F dotted with (rx X ry) dA

Convert to polar coordinates to finish it off (note I already put the limits of integration in polar form, but like, if you see an x in the equation, it becomes rcos(theta), etc...

I have taught you well, grasshopper.

Damn, that boy is LEARNED.....I didn't even have the attention span to read the entire problem let alone give any sort of explaination. Eh well, you start working in the real world, you start forgetting things. Hope all went well chief!!