Mechanical Principals Assignment Question

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  • #26
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1a. Looks OK to me.
1b. Wrong units for strain. Strain is dimensionless (and in this case negative).
1c. Be careful with signs and units. 0.002121 is not equal to -2.121 x 10-3. And -2.121 x 10-3 what? You are mixing units too much, and getting confused. I would convert everything into m (and Pa etc.)
1d. Change in length is not 7.75. What length is being referred to? (Why don't you just do it like 1e?)
1e. OK, but what are the units of the answer?
1f. As there is no Fig 2, this is impossible.
As for Question 1f, I assume I have a running pattern of being completely wrong, but here is the FIG 2 I failed to initially post.

upload_2017-1-6_11-16-50.png

And my Answer?
upload_2017-1-6_11-30-37.png
 
  • #27
mjc123
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Looks correct to me.
 
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  • #28
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Great! I am just working bac through my assignment now and correcting where I have made mistakes.
I have one more Question if you could help me? it is only a 1 part question but I have a Negative answer for my Bulk modulus? im not sure I should have a Negative answer.
upload_2017-1-6_13-31-47.png

My Answer is:
upload_2017-1-6_13-32-26.png
 
  • #29
mjc123
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Careful with units again here! The volume is 5.24 x 105 mm3 - not m3. Fortunately in ΔV/V the units cancel out. Its value is -3.817 x 10-3 NO UNITS!!
You have missed out a negative sign from the definition of bulk modulus. When you compress a body the volume decreases, so the bulk modulus is defined as
K = -VdP/dV
1047.94 MPa is the right answer (but too many sig figs), but this is not equal to 1.5 GPa but 1.05 GPa.
I don't want to sound hectoring, but as I said before you are making problems for yourself by being careless. One characteristic of a good scientist or engineer is attention to detail. Be careful about copying equations and calculations accurately, including signs. And pay careful attention to units. Get into the habit of thinking of a quantity as number plus unit, not just number (unless it happens to be dimensionless). It is never right to say that e.g. the length is 10. 10 what? metres, mm, miles, Angstroms? And be careful about mixing units, e.g. dividing MPa by GPa. It may be helpful to write the units in your calculation, e.g. 7 MPa/200 GPa rather than 7/200 and try to remember to correct for the conversion factor. Or convert everything to the same units before doing the calculation.
 
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  • #30
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I cant thank you enough for your help with all of this. This time last year I was just starting the course and I have had to learn everything from scratch. I hadnt touched algebra in 16 years and there was no explanation behind the reason why engineers use x10^3 as apposed to x1000. I have learnt most of the methods I use by searching outside of the e learning and sifting through forums and youtube videos, Therefore there have been gaps in my education hence the reason I make mistakes alot.
I have a hundred questions I could ask you but I wont take up all of your time. Thanks again for your help!
 
  • #31
I cant thank you enough for your help with all of this. This time last year I was just starting the course and I have had to learn everything from scratch. I hadnt touched algebra in 16 years and there was no explanation behind the reason why engineers use x10^3 as apposed to x1000. I have learnt most of the methods I use by searching outside of the e learning and sifting through forums and youtube videos, Therefore there have been gaps in my education hence the reason I make mistakes alot.
I have a hundred questions I could ask you but I wont take up all of your time. Thanks again for your help!
Hello, by any chance do you have an answer to question 2 for this assessment?
 
  • #32
mjc123
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I can see a question 1 and a question 3, but no question 2.
 
  • #33
I can see a question 1 and a question 3, but no question 2.
Yeah Q2 isn't on the thread I was just asking if he had completed the question I'm guessing so, as this thread is pretty old.
 
  • #34
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Yeah Q2 isn't on the thread I was just asking if he had completed the question I'm guessing so, as this thread is pretty old.
Yes I did complete question 2 but the whole point in this type of learning is find out the answer by making an attempt as apposed to asking if someone will give you the full answer for free. If you understand the subjects you are studying you will help yourself in future assignments when you come across similar questions.
 
  • #35
Yes I did complete question 2 but the whole point in this type of learning is find out the answer by making an attempt as apposed to asking if someone will give you the full answer for free. If you understand the subjects you are studying you will help yourself in future assignments when you come across similar questions.
If you could just jump off your high horse for a second, you seem to have miss understood me just like the person who was helping you out above. All I wanted to do was compare my answer for Q2 with a person who has taken the same question. Don't worry too much I submitted the assignment this afternoon sure I got the correct answer.
 
  • #36
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Hello, by any chance do you have an answer to question 2 for this assessment?
Forgive me for riding my high horse. But this does sound simply like you have asked me by any chance do I have an answer to question 2 for this assignment. Without you onces previously saying, I have made an attempt at this one can you offer any advice.

Well anyway good luck! I got a distinction for my efforts hopefully you will do too.
 
  • #37
Forgive me for riding my high horse. But this does sound simply like you have asked me by any chance do I have an answer to question 2 for this assignment. Without you onces previously saying, I have made an attempt at this one can you offer any advice.

Well anyway good luck! I got a distinction for my efforts hopefully you will do too.
Well done, hopefully I will but id be more than happy with a merit. Thanks
 

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