Find the total mass of a wire with a certain density ?

CalleighMay

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Hey guys! I have been on the forum for about a week or so and have compiled a lot of information and techniques to help me understand calculus, so i really appreciate everyone's help!

I am a soon-to-be freshman in college and am taking a summer class, calculus II (took calc I in HS). This is our last week of class after our final exam so my professor is taking this time to give us a preview of what we will be learning in the fall semester in Calc III (since this is the same professor). Every Tuesday class our professor gives us a few problems from future sections and asks us to "see what we can come up with" and to work together to find solutions. The following Tuesday he asks us to discuss the problems as a class, seeing which ones of us know our stuff =P

Basically, i want to ask you guys what you think about these problems as i do them along before i have my discussion. I really want to make a lasting impression on my professor by "knowing my stuff" -to show him i can do it! All's i need is a little help! Would you guys mind giving me some help?

We are using the textbook Calculus 8th edition by Larson, Hostetler and Edwards and the problems come from the book.

The problem is on pg 1075 in chapter 15.2 in the text, number 26. It reads:

Find the total mass of the wire with density p.
And it gives:
r(t)=2 cos ti + 2 sin tj + 3tk
and p(x,y,z)=k+z
(the p is a different looking p, most likely represents something else, something that sounds like roe maybe? lol. and k is really k below)
and: (k>0), 0<=t<=2pi


I looked at similar problems in the same section and came up with the following for this one:

r'(t)=2 cos ti =2 sin tj
but when finding II r'(t) II how do i do this with sin and cos? I know it's sqrt of each term squared, so would it be: sqrt( 2cos^2t - 2sin^2t ) ?

Then at this point, even if the above was correct, it's telling me to do:

integral from C to ? of p(x,y,x) dx and integral from C to ? of kz ds

Yeah i'm lost!!! :( Any further help would be greatly appreciated. Thanks guys! =/
 
\(\displaystyle r'(t)=-2sin(t)i+2cos(t)j+3k\)

\(\displaystyle ||r'(t)||=\sqrt{13}\)

\(\displaystyle \text{Mass}=\int {\rho}(x,y,z)=\sqrt{13}\int_{0}^{2\pi}(k+3t)dt\)
 
thanks galactus! Should i be getting a numerical answer? Or do i leave this the way it is?
 
You should take stapel's advice and quit playing games - in favor of actual studies and knowing what you are doing. Just guessing is not a good business.
 
i'm not trying to play games here, i honestly don't know what i should be looking for here. I looked at the answers to similar problems and the work does not look like what has been provided... I'm just asking if someone can explain what they have done.

I'm sorry if i am wasting everyone's time... i'm just trying to get ahead in the time frame that i have.
 
CalleighMay said:
i'm not trying to play games here, i honestly don't know what i should be looking for here. I looked at the answers to similar problems and the work does not look like what has been provided...
As has been repeatedly explained, what you "should be looking for" is the content of your text, and whatever other texts, online resources, and other tools you are using. Trying to "back-engineer" integral calculus from a few hints or an example or two is not how to learn the material. To learn this, you will need to spend a few hours a day in study.

CalleighMay said:
I'm just asking if someone can explain what they have done.
Your book "explains" what it has done, but you haven't read that. Other posts have had complete worked solutions provided, but you haven't studied them enough to even be aware that you've been given the answers.

Really, at some point, you need to start investing a little effort into the process. We await your intelligent, studied, thoughtful, and informed reply, showing your understanding and your efforts.

Eliz.
 
Eliz, i have 3 hours left before discussion, i understand it's a short amount of time, but be that as it may i am merely asking for your help in the solution so i can present something to my group. It is not graded, to be honest no one else is giving these problems a second of their time.

I don't expect you to be able to "teach" it to me in such short time, nor would i ever expect to teach myself via the book in such a short time either.

If you cannot, or feel bad about giving me the solutions, then don't. It's not urgent or going to change my life either way. I am only trying to go to class with something other than what i could come up with by myself (which is nothing). You don't need to make me feel bad about it...

I understand your position, i am merely asking for all you feel comfortable offering at this time. Thanks...
 
Hey guys, can someone give me the full solution please? We had class last night and he didn't really explain them but i would like to know the answers.

Thanks!
 
CalleighMay said:
Hey guys, can someone give me the full solution please? We had class last night and he didn't really explain them but i would like to know the answers.

Thanks!
You have to show us that you are at least trying - and are capable of attending these classes that teach at this level.

The copy of the book that I have (2 nd edition) has very good example problems - almost exactly like the problem posted - I would assume 8 th edition will have similar/same example problems.

Read through those - copy one of those problems onto these pages to show that you are at least looking at those - then I would work with you....
 
CalleighMay said:
shouldn't there not be a k in the mass equation? (k+3t) ?

That is a straight-forward integration - and you cannot do that while taking multi-variable calculus!
 
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