I'm trying to finish hw#7, i have y0 and the chart filled in but i dont have y', yt, or the maple thing. If someone can help me with some of that i would be happy to help with the rest.

3/1/2006 4:34:58 PM

you're gonna need to post the problem.

3/1/2006 4:36:00 PM

everyone in this class should have the same webassign so they should all have a copy of the same problems, just with different numbers. If someone has the answer they can just post it and anyone can fill in their own numbers to the given equation

3/1/2006 4:41:35 PM

oh...i get it.

you think everyone who has ever had the class should remember the details of all the assignments
chances are, if you don't post the problem, you will not get any help. So, suck it up and post it, or hope for the best

3/1/2006 4:48:35 PM

actually i was just catering to my target audience, i was assuming that people not in the class wouldnt respond to my resquest, but ok if you want the peoblem here is one that i am missing: initial temp = 210, room temp = 70, k = 1/16, what is the continuous solution equation? (use t as variable) thanks

3/1/2006 4:58:54 PM

Quote :

"actually i was just catering to my target audience, i was assuming that people not in the class wouldnt respond to my resquest, but ok if you want the peoblem here is one that i am missing"

Folks will help you, if they can, regardless of whether or not they're currently enrolled in the course.
Also, for future reference, the best way to post any WA problem is to take a screen shot of it, add it to your gallery, and post it in the thread (done by right clicking the picture for the location, and then using the 8th button from left in the reply to topic window)
That said, I have yet to take MA 132, and all I know about the course is that it's held in G108, and that it's primarily an excel course
Thank you for not being a cocky n00b about this

3/1/2006 5:04:19 PM

Quote :

"initial temp = 210, room temp = 70, k = 1/16, what is the continuous solution equation? (use t as variable) thanks"

Lets see I think the equation here is that the rate of temperatur change dT/dt is proportional to
the difference from room temperature (T-70) according to the proportionality constant k=-1/16. That gives us the differential equation:

dT/dt = k(T-70)

Seperate variables,

dT/(T-70) = kdt

Integrate,

ln|T-70| = kt + C1

Exponentiate,

|T-70| = exp(kt+C1) = C2*exp(kt)

This allows for two possible families of solutions, one where |T-70|<0 and another where
|T-70|>0. Using +/- notation for this gives us

T- 70 = (+/-)C2*exp(kt)

Solving for T and introducing C3=(+/-)C2,

T= 70 + C3*exp(kt)

Now we know that T(t=0) = 210 = 70 +C3 thus C3= 140. Hence,

T = 70 + 140*exp( (-1/16)*t )

Notice that as t goes to infinity we reach room temperature.

3/1/2006 6:14:44 PM

^well done kid, well done. I was gonna offer help, but you covered damn well.

3/1/2006 6:31:38 PM

thanks mathman, now the only part im missing is the maple part at the end, and i have no idea how to use that program at all, better yet create a chart using it. If someone could send me the file they created and i could use it as an example/ change the numbers that would be great. (still in reference to webassign hw#7)

I cant really think of a way i can post this question so people not in the class can help

[Edited on March 1, 2006 at 6:33 PM. Reason : asdf]

3/1/2006 6:32:16 PM

^mmm... sounds to me like maybe you should go to class........
since the problems are basically handed to you already done, just put in your numbers

3/1/2006 6:48:42 PM

^^Maple,... ick that's cheating.

3/1/2006 6:51:00 PM

Quote :

"^mmm... sounds to me like maybe you should go to class........ since the problems are basically handed to you already done, just put in your numbers "

She knows what she's talking about... Somebody begged the instructor to do an example for the Maple portion of the WebAssign, and he basically did the whole thing for us, no questions asked. I had the damn thing done before I left the room!

Anyway, the commands you should need are below. You'll probably need to change the numbers around in the third command, since I believe my problem was different from your's:

diffeq:=diff(y(t),t)=-k*(y(t)-yr);

solution:=dsolve({diffeq,y(0)=y0},y(t));

solution2:=subs(yr=70,y0=207,k=1/15,rhs(solution));

plot(solution2,t=0..60);


[Edited on March 1, 2006 at 7:49 PM. Reason : .]

3/1/2006 7:36:20 PM

thanks i really appriciate it, thats gonna save me a ton of time

3/1/2006 8:09:06 PM

no, but seriously, go to class. in the time it took to get responses to do the work, you could have done it in less than 50 mins..... in class.

3/1/2006 9:48:56 PM

i always end up goofing off on the web when i go to class.

our absenses don't matter as long we make 100's on the webassigns right?

3/2/2006 1:29:56 PM

I dont know about the absence thing, i thought they counted even if you are getting 100's, that would be good to know though, im in the class at 8:05 so its a bitch to get up for that

3/2/2006 2:48:05 PM

its that time again to start thinking about webassign, im starting on hw#8 right now, once i get some answers ill post them, anyone else with some success it would be appriciated if you do the same.

3/15/2006 4:51:58 PM

i took the class last year..i was in the 8 am..never went to a class and got 100's on all webassigns..i ended up getting an A+ (99 i think, took 1 pt off because i missed the first class)

3/15/2006 5:16:57 PM

absences don't matter...i've been to 1 class this semester and i've already done the homeworks through mid april hahaha

3/15/2006 5:46:03 PM

ok turns out this one was pretty easy so if anyone has a problem with hw#8 they can ask otherwise im off til the next one

3/15/2006 8:29:56 PM

Does anyone know if they actually check the attached excel or maple files? I've been doing them so far far, but they seem like a waste of my time. Also, I'm just starting hw#9 and am having a problem getting the equation to submit. I think I have the right equation I must just be putting it in wrong. Can someone post theirs and I can base mine off of that?

3/21/2006 7:35:58 PM

Are you using "exp" to denote the "e" value?

The equation should be set up like this: y(t) = y(0)*exp(rt)

3/21/2006 7:51:46 PM

thanks that helped, i was leaving out the * before the exp, now for the rest...

3/21/2006 9:23:54 PM