 |
| الكاتب | ارسال |
|---|
justdrawinglines
Member
| تاريخ الالتحاق: | الجمعة أبريل 6th, 2007 |
| الموقع: | ARCHITECT, New York USA |
| عدد المواضيع: | 637 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | failure WAS NOT an option - SUCCESS AT LAST!!!! |
| Status: |
Offline
|
| مستوى: |    |
|
كتب: الاحد أوكتوبر 19th, 2008 10:06 pm |
|
Okay, so there's a question on the Kaplan test bank CD (2006). I've worked it a few times and keep coming up with the same answer, which isn't a choice from A to D...
Would someone mind working this bugger out and show me what I'm doing wrong? I keep getting 30,745.8 [edit] P using delta L = PLo/AE.
A steel bar 1-1/2" in diameter and 25'-0" long stretches 0.18" when subject to a load. If the modulus of elasticity E is equal to 29,000,000 psi, what is the unit stress in the bar?
A. 20,880 psi
B. 17,400 psi
C. 36,000 psi
D. 10,191 psi
Thanks!
اخر تعديل في الخميس أوكتوبر 23rd, 2008 05:17 pm بواسطة justdrawinglines
|
Marc Mitalski w/ PREPA.R.E., Inc
Member
| تاريخ الالتحاق: | الاثنين نوفمبر 22nd, 2004 |
| الموقع: | Illinois USA |
| عدد المواضيع: | 145 |
| Exams Taken: | | | Exams Passed: | | | Describes Me: | |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الاحد أوكتوبر 19th, 2008 10:23 pm |
|
Hi justdrawingslines,
I came up with B - 17,400 psi as the answer
Hooke's Law - Delta = PL/AE
Delta (given) = 0.18"
L (orginal length, given) = 25'(12"/ft) = 300"
E (given) = 29,000,000 psi
A can be be solved for based on the information given but is not needed
They are asking for the unit stress, which is P/A, so....
0.18" = (P)(300") / (A)(29,000,000 psi)
rearranging the equation above and solving for P/A
P/A = (0.18")(29,000,000 psi) / 300"
P/A = 17,400 psi
Marc
|
justdrawinglines
Member
| تاريخ الالتحاق: | الجمعة أبريل 6th, 2007 |
| الموقع: | ARCHITECT, New York USA |
| عدد المواضيع: | 637 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | failure WAS NOT an option - SUCCESS AT LAST!!!! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الاحد أوكتوبر 19th, 2008 10:47 pm |
|
Thanks, Marc.
I feel like I'm never going to get these calcs straight... What can I do to remember things like, "well, for this I don't need to plug in the area of the bar"? My thought process on this one was go straight to delta L = PLo/AE, and by all means pass F=P/A because there's not enough info to go there... Am I missing something?
Maybe it's because I've been at this since 7am.
oy...
|
justdrawinglines
Member
| تاريخ الالتحاق: | الجمعة أبريل 6th, 2007 |
| الموقع: | ARCHITECT, New York USA |
| عدد المواضيع: | 637 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | failure WAS NOT an option - SUCCESS AT LAST!!!! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الاثنين أوكتوبر 20th, 2008 01:14 am |
|
Okay, so I just had a "doh!" moment...
Basically, by ignoring the value of A you save a step. If I had just divided my result (the value of P) by A and hence the correct units, I would have gotten where I needed to be - 17,400 psi.
My head hurts.
اخر تعديل في الاثنين أوكتوبر 20th, 2008 02:39 pm بواسطة justdrawinglines
|
fibes
Member
| تاريخ الالتحاق: | الاثنين أبريل 28th, 2008 |
| الموقع: | Architect, Georgia USA |
| عدد المواضيع: | 221 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Architect, musician, producer, nut job. |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الاثنين أوكتوبر 20th, 2008 03:38 pm |
|
This was a step i had a hard time with due to my lack of Algebra brain cells.
I just flat out remembered "change" times the 29 thingy over size = what I'm stressing about.
Remeber the 29 thingy changes with kippers and pounds and yer good.
Still waiting on my results, it's 2 weeks today.
اخر تعديل في الاثنين أوكتوبر 20th, 2008 03:40 pm بواسطة fibes
|
skyhook
Member
| تاريخ الالتحاق: | السبت مارس 15th, 2008 |
| الموقع: | BT Or Bust |
| عدد المواضيع: | 1020 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP | | Describes Me: | support where beam or wall not available |
| Status: |
Online
|
| مستوى: | |
|
كتب: الاثنين أوكتوبر 20th, 2008 03:51 pm |
|
I focused 85% of my study on concept reading, then crunched my brains with the basic calc memorization of 1/2 dozen functions or so, right before the test. Calcs blows, but this plan worked for me. Whether studying or testing, I actually picked up bonus answers by saving the calcs until the end of test (or study time).
Good luck Lines.
اخر تعديل في الاثنين أوكتوبر 20th, 2008 03:53 pm بواسطة skyhook
|
justdrawinglines
Member
| تاريخ الالتحاق: | الجمعة أبريل 6th, 2007 |
| الموقع: | ARCHITECT, New York USA |
| عدد المواضيع: | 637 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | failure WAS NOT an option - SUCCESS AT LAST!!!! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الاثنين أوكتوبر 20th, 2008 04:25 pm |
|
Thanks, sky and fibes. This one is killing me. Planning on the first week of November, and still debating on whether or not to cram for LF and do them the same day.
And for anyone debating on Marc's on-line anytime - DO IT! Granted, I'm still confused here and there... but without the seminars and the time Marc spent with me on the phone, I would be totally lost.
|
MACVILLE
Member
| تاريخ الالتحاق: | الاربعا يوليو 19th, 2006 |
| الموقع: | Illinois USA |
| عدد المواضيع: | 159 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Done Done Done! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 03:04 pm |
|
Marc Mitalski w/ PREPA.R.E., Inc wrote: Hi justdrawingslines,
I came up with B - 17,400 psi as the answer
Hooke's Law - Delta = PL/AE
Delta (given) = 0.18"
L (orginal length, given) = 25'(12"/ft) = 300"
E (given) = 29,000,000 psi
A can be be solved for based on the information given but is not needed
They are asking for the unit stress, which is P/A, so....
0.18" = (P)(300") / (A)(29,000,000 psi)
rearranging the equation above and solving for P/A
P/A = (0.18")(29,000,000 psi) / 300"
P/A = 17,400 psi
Marc
This one cofuses me too....why wouldn't I put A in if it's given (or easy enough to solve for?!)
|
MACVILLE
Member
| تاريخ الالتحاق: | الاربعا يوليو 19th, 2006 |
| الموقع: | Illinois USA |
| عدد المواضيع: | 159 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Done Done Done! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 03:07 pm |
|
| never mind....I used A and still got the right answer.
|
justdrawinglines
Member
| تاريخ الالتحاق: | الجمعة أبريل 6th, 2007 |
| الموقع: | ARCHITECT, New York USA |
| عدد المواضيع: | 637 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | failure WAS NOT an option - SUCCESS AT LAST!!!! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 05:07 pm |
|
How could you have gotten the correct answer if you included the value of A in the original equation - delta L = PLo/AE? If you did that, which is what I originally did, your answer is P = 30,745.8. Which is not the answer to the question - the unit stress. I ignored the actual question (what is the unit stress?) because I got caught up in the equation - delta L = PLo/AE. All they are asking for is P/A....
Am I still not getting this? Marc, Help!
اخر تعديل في الخميس أوكتوبر 23rd, 2008 05:16 pm بواسطة justdrawinglines
|
MACVILLE
Member
| تاريخ الالتحاق: | الاربعا يوليو 19th, 2006 |
| الموقع: | Illinois USA |
| عدد المواضيع: | 159 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Done Done Done! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 05:11 pm |
|
I TOOK :
018"=300P/1.767x29,000,000
AND THEN SOLVED FOR P AND I GOT 17,399....NOT SURE HOW DUMB LUCK WOULD HAVE GOTTEN ME THE RIGHT ANSWER....
|
MACVILLE
Member
| تاريخ الالتحاق: | الاربعا يوليو 19th, 2006 |
| الموقع: | Illinois USA |
| عدد المواضيع: | 159 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Done Done Done! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 05:18 pm |
|
| oh wait.....man i don't know what i did...........sorry. i got the 30,000 answer that time too!
|
justdrawinglines
Member
| تاريخ الالتحاق: | الجمعة أبريل 6th, 2007 |
| الموقع: | ARCHITECT, New York USA |
| عدد المواضيع: | 637 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | failure WAS NOT an option - SUCCESS AT LAST!!!! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 05:19 pm |
|
whew.... glad to know I'm not THAT braindead because of this exam!
|
MACVILLE
Member
| تاريخ الالتحاق: | الاربعا يوليو 19th, 2006 |
| الموقع: | Illinois USA |
| عدد المواضيع: | 159 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Done Done Done! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 05:23 pm |
|
yeah, no clue why i got 17399 that first time! must have been a slip on the good old windows calculator!
now if i leave out the A variable i get the 17400psi. i guess if you keep getting an answer thats not listed then take A out of the equation and try it that way!
|
sharcitect
Member
| تاريخ الالتحاق: | الاحد أوكتوبر 14th, 2007 |
| الموقع: | NYC |
| عدد المواضيع: | 239 |
| Exams Taken: | | | Exams Passed: | | | Describes Me: | A-R-C-H-I-T-E-C-T |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 05:59 pm |
|
An attempt to clarify:
The trick is they are asking for the stress (P/A) and we are fooled into trying to solve for the actual load on the bar (P)... If they had left out the diameter of the bar, this problem would have been easier to solve. By giving us too much information, we tend to answer more than what is being asked. If you take your result for P (30,745.8) and divide it by A you will have the answer they were looking for...
If they left the diameter of the bar out of the question, we wouldn't be able to solve for P, only for P/A.
It would have been particularly nefarious if they had included 30,745.8 as a possible answer. I guess this is a good lesson for us (I definitely got this wrong until I saw Marc's response) to re-read the question carefully if our answer doesn't match any of the possible answers.
Does that make any sense?
|
MACVILLE
Member
| تاريخ الالتحاق: | الاربعا يوليو 19th, 2006 |
| الموقع: | Illinois USA |
| عدد المواضيع: | 159 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Done Done Done! |
| Status: |
Offline
|
| مستوى: | |
|
كتب: الخميس أوكتوبر 23rd, 2008 06:03 pm |
|
OHHHHHHH, YEP.. WHEN I LOOK BACK AT MY CHICKEN SCRATCH..THERE IT IS ON THE SIDE F=P/A! THATS HOW I GOT IT!
VERY GOOD EXPLANATION SHARCITECT!!!!
|
الوقت الحالي هو 08:38 pm | |
|
|
|
|
