I'm trying to start the HW and I thought I was doing alright till I looked in the back of the book at the answer for 1.7. Anyone know how to do this one? Also post any other questions or comments about the first HW.

8/22/2005 7:27:15 PM

when is this HW due? wednesday?

8/22/2005 7:44:25 PM

you know he never really said, so i dont think it would be weds. i dont think hes covered everything to do all of it yet.

8/22/2005 7:51:21 PM

he didnt even mention anythin today about it so i'm sure most people dont even know

8/22/2005 7:53:29 PM

yeah prob not

8/22/2005 7:58:32 PM

imma bout to start that one.

8/22/2005 8:26:38 PM

well let me know what you come up with

8/22/2005 9:20:53 PM

i got somethin but no where near what the book has. and i dont see what i did wrong either.

8/22/2005 9:32:56 PM

i moved on to the 2nd problem...anyone else get the right answer without worrying about the 50% reduction?

8/22/2005 9:50:01 PM

^^ yea i got something that was a long, but it wasnt same as book. im gonna try it again tomorrow

8/22/2005 9:52:23 PM

where is the class website?

8/22/2005 10:45:27 PM

there is none yet. just the syllabus he emailed us.

8/22/2005 10:53:05 PM

http://courses.ncsu.edu:8020/mae315/common/media/

http://engineeringonline.ncsu.edu/onlinecourses/coursehomepages/fall05/MAE315.htm

8/22/2005 11:04:53 PM

This sucks, first problem in the class and its that tough

8/22/2005 11:40:29 PM

are you kidding? MAE 315 is a bitch of a class, but the first stuff you cover (single DOF, undamped systems) is some of the most elementary stuff i remember doing in ME.

also, the last quarter or so of that class isn't too bad. the middle half is a real pain in the ass, though.

Dr. Ro might be the best professor in the dept (which admittedly doesn't say much) in terms of being able and willing to assist you in his office hours. GO TO HIS OFFICE HOURS. i know it's a waste of time with most professors, but it will help you immensely in this case.

what's the problem? i haven't messed with that stuff in a few years, but if its 1 DOF, undamped, it can't be that hard.

8/23/2005 2:15:32 AM

HW1 is due monday 8/29. i emailed him and asked him. also, no TA yet either.

the 1st problem is a spring constant problem where there is a system of like 7 springs and u have to find the equivalent spring constant using series and parallel methods.

[Edited on August 23, 2005 at 7:44 AM. Reason : .]

8/23/2005 7:43:25 AM

whats the question number in the book?

8/23/2005 9:35:44 AM

Problem 1.7

8/23/2005 10:04:50 AM

scan the problem and upload it, and i'll tell you how to do it.

8/23/2005 1:09:25 PM

8/23/2005 1:41:43 PM

whoa, thats one heck of a problem. maybe i should get started on this HW

8/23/2005 2:00:40 PM

has anyone made progress on this homework?

8/23/2005 4:48:36 PM

If you remember nothing else, remember spring constants for springs in series add inversely [(1/k1)+(1/k2)]^-1 = keq and springs in parallel add straight up k1+k2 = keq. To determine if two springs are in parallel or series, insert a solid link. If the other spring can still move, the springs are in series.

In 1.7, the two k1's at the top are in parallel, giving an equivalent spring constant of 2k1.

8/23/2005 6:00:02 PM

well im skipping that one. i dont know what im doing wrong

8/23/2005 6:50:28 PM

how i did it: k1+k1=2k1 because of parallel. likewise, k3+k3=2k3 due to parallel. i then said "1/keq = 1/2k1 + 1/k2 + 1/2k3" because all 3 are in series. once i did that i solved for keq so that i could add keq and k4 due to parallel. then after that, the new k and k5 are in series. once again i used the the "1/keq" process. i got an answer but no where near what the book has. my error has to be in my math and i'm just not seeing it.

8/23/2005 7:02:55 PM

thats what i did too

8/23/2005 7:03:47 PM

What about the other ones? Anyone getting anywhere on those?

8/23/2005 7:19:30 PM

not really. it would be nice if there were solutions online, but atleast he doesnt grade on correctness.

8/23/2005 7:55:05 PM

That sounds like the right process.

This is what I got:

This is the book solution:


[Edited on August 23, 2005 at 9:46 PM. Reason : ]

8/23/2005 9:40:19 PM

Thanks for posting the answer.


It's just a cluster fuck of K's, but I got it. Well...my equivalent rate comes out with the same number when I plug them into my solution and the book's answer.


Just do a pair or springs in series or parallel at a time.




Now someone scan the other problems so I can do them. Hahah. I'll go buy the book tomorrow. Promise.

8/23/2005 9:54:16 PM

n/m..i wasnt adding fractions right

[Edited on August 23, 2005 at 10:40 PM. Reason : .]

8/23/2005 10:33:38 PM

thanks. i forgot how to add.

8/23/2005 10:45:28 PM

yea i just cant add and multiply fractions right...i had it right except 1 step which fucked the whole rest up

8/23/2005 11:01:29 PM

anybody have luck on any others? Will be working on this in the brary tomorrow probably after class if anyone is interested

8/23/2005 11:12:08 PM

havent gotten anywhere really on the others. gonna be workin on it more this week. for those who need the problems:

1.10b

1.34

1.35a,b,c

[Edited on August 23, 2005 at 11:15 PM. Reason : .]

8/23/2005 11:15:01 PM

On the last one (1.35) a and b are found derived in the text. its just like with the springs in parallel and series. then part c is found using a method found on pg 31. In the example it uses masses but its the same thing. put your c in instead of m

8/23/2005 11:23:53 PM

I just wish we didn't have so many technical problems being in park labs

8/24/2005 11:12:09 AM

well have fun in that class. I had to drop it.

8/24/2005 6:13:43 PM

y did u drop it

8/24/2005 6:28:36 PM

for scheduling reasons having to do with my co-op

8/24/2005 11:36:57 PM

Ok the only one I don't really know how to do is 1.34. Anybody know how?

8/25/2005 10:45:12 AM

just a friendly heads up....ro has quite a few past hw solutions posted on the library e-reserve.

8/25/2005 11:00:27 AM

its actually an easy problem. expect a few things like this on at least 1 test.
look for all the eqns that have a mass or rotational mass in it, and set the sum of them equal to 1/2Meq*x²

so that
1/2Meq*x² = 1/2*Jsphere*THETAsphere² + 1/2*Ms*Xs² +... et. cetera. divide by 1/2 to make it less ugly, then convert all of the THETAs into functions of X.

helpful relations: X=THETA*L1
Xs=THETA*L2.
Xs=THETAsphere*Rs

8/25/2005 7:22:52 PM

I was rather disappointed that this class as well as my 301 classes got switched to Eonline in Parks

8/25/2005 8:18:40 PM

anybody started on the HW2 yet?

8/31/2005 9:21:54 PM

bttt for set 2. anyone get anywhere with this yet?

9/5/2005 5:58:53 PM

I actually did the first two without getting stuck. The rest? Ehh. I've got something written down for them, but none of them are complete.

9/5/2005 6:04:43 PM

yea same here. some of them i'm just wtf on esp that ratio problem where ur given the ratio 18:1 and u have to find the new ratio. i mean ur given like zero info. maybe i'm just not seein somethin really simple.

9/5/2005 6:07:22 PM

bttt

9/6/2005 12:51:34 PM

set em up

9/6/2005 1:02:18 PM