Ch 14.3 Help

Sorry, last post. Just for forgot to say that you remove the spaces in the link, in case some people have never done this before.

i love you guys

Im still not gettin number 4. Can someone please explain again with numbers. Is it positive or neg?

that link isnt working even when i copy past....boooo

i enter the numbers but it is not showing me the answer,what do i have to do??? please help

So, I basically just followed what was posted on the blog but I'll fit it with my question

A refrigerator in a room at 15 oC keeps the temperature in the freezing compartment at -2 oC. If the real "coefficient of performance" is the ideal one divided by 1.817 and 341.8 W are released into the room what is the power use of the compressor

TH = 15 + 273.15 = 288.15 K
TL = -2+273.15 = 271.15
e_real = e_ideal/1.817
Q_H = 341.8 W

c.p_ideal = (271.15)/(288.15-271.15) = 15.95
c.p_real = (15.95)/(1.817) = 8.778
c.p = Q_L/ Q_H - Q_L
You want to solve for Q_L here so get it all on one side
c.p(Q_H-Q_L) = Q_L
c.p*Q_H - c.p*Q_L = Q_L ( i multiplied out the parentheses)
c.p*Q_H = c.p*Q_L * Q_L
Now remember, c.p = 8.778, Q_H = 341.8
(8.778)*(341. = (8.778*Q_L)+(Q_L) -> if you remember math, when there is no number in front of a variable it is just considered to be a one, so you add the two Q_L's together
3000.39 = 8.778*Q_L + 1*Q_L
3000.39 = 9.778*Q_L
(3000.39/9.778) = Q_L
Q_L = 306.8447

Now, I don't really know why we are doing some of this stuff, I just worked off of someone elses work when I couldn't figure it out myself...but now you do

W = QH-QL
W = 341.8 - 306.8447
W= 34.95

Answer is positive
this worked on maple TA for me, and I tried it out on the problem posted above so i hope it works for you guys.

Just enter the numbers and click enter. The answer is under the "Answer" tab. I'm not with my laptop right now so I'll check when I get back if it's working or not.

I don't know why that smiley face showed up but that number is just the 341.8 (QH value)

u guys are the best

thank u for posting and not being jerks...
i don't learn anything from class...

when u guys put explanations, I actually get them...


*good luck on finals everyone. =)

I hope the professors realize how this website is really helpful.

i was just wondering how you find the sendspace excel sheets for other quizzes...if there is some sort of SBU site for physics?...

Interesting that the day I decide to check you guys out again I find a comment wondering we realize how useful the site is!

As some of you know I have posted on here some time ago. I have never tried to discourage this site and I can actually see that the site is for the most part useful and there are real explanations here. If you are actually following those and learning from them then I don't have a problem As you know we run our own blog as well which I hope you have also found useful.

But... I see you have a new feature..and this I really don't like

Can anyone seriously say that plopping numbers into an Excel Spreadsheet is going to help you learn how to tackle problems?

It's also going to make the argument I hear all the time of "Well I do well on all the homework so I don't understand why I did so badly on the exam" sound pretty unconvincing!

Be wise here..if everyone gets full marks on the assignments then the grades are all going to be based on the exams...and I'm pretty sure that the people actually doing the problems themselves are going to score higher on the exam..So don't fool yourself that you are helping your grade (which I know is the biggest concern for most of you) by taking shortcuts on the homework.

Please believe when I say we don't give homework to make your life miserable, its actually intended to help you learn the material!

Good luck to everyone on the exam!
(Hint: To do well, make sure you have lots of practice solving problems WITHOUT anyone there to help you! )

I do not know about many of the other visitors to this site but I think most of us here see that the Excel file and the poster for it, as spam and a spammer. Perhaps it is a virus, perhaps it is legit but do I really need excel to find out?

The work here, and most explanations are shown, so is it a necessity to have such a program? I think not. Generally I feel it's quicker to solve these problems when you know what they are asking rather then plug in numbers. I've done quizzes in 6 minutes, will it really shave off any time?

All I'm saying, is that I agree with you Professor Dawber. I post here and come here for help, as I do the same for the blog, however some of us feel more comfortable asking our peers, or find it silly to ask certain questions on a blog which may not correlate to the given topic. Professor(s) we understand that you, just like ourselves are busy. For many of you this is a second job, your first being researches (I mean after all we go to a research University). In this hectic campus of ours it is good to have many resources, this forum is nicer because there may be other users on here which can "answer" us faster then the blog where the only correct answer can come from the head(s) of the course.

And with this rant I also agree with you because on the last few chapters I see questions which have been answered many times, often under the same topic! Or other times it is the same procedure or ideas which people only ignore. What really set me off was a few weeks ago when I saw someone asking the units for velocity. This made me truly sad.

And then again I am far from having the best grade in the class. I do understand most of the work, I have explained many of the solutions on here, but perhaps I am just bad at test taking. With that, and the utter ignorance to the learning procedure I find myself very upset of where I am and where I should be.

For all those who have read, godspeed and god help us all.

Please do not speak for everyone and assume they have the same opinion as you. It would take 5 seconds to figure out this person is not a spammer and this is not spam. And that's about as long as it takes to do the quiz using the excel The file type is an Windows 2007 excel file and i don't know how anyone could confuse it with a virus. Let's not throw words around that we don't know how to use. And as to the intentions of the individual, I would give him the benefit of that doubt that he did not intend to wreck the grading scheme but help people that did not want to be punished for not doing the quizzes. Why can't the quizzes be optional and the individuals who want to do well in the class can do them and do well on the exam and then individuals who want to do poorly can ignore them and do poorly on the exams. As to the rest of your post, I didn't read it cus it was long.