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Finding the third force on a bracket when given the first 2 forces and the resultant

  • Thread starter Popa91
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  • #1
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Hi everyone, i came across this forum a while ago and have been lurking here for a while. Any ways, i have a simple problem but cant seem to find a solution to it the photo of the problem is the link just here

http://i1053.photobucket.com/albums/s463/Popa911/1cc85138.jpg

Homework Statement



Three cables exert a force on a bracket (as shown in the photo) F1=300N, F2=500N and the resultant is 400N and 30° downward from x.



Homework Equations




the equation i used to solve was Fr=F1+F2+F3 rearranged to get F3= Fr - F1 - F2


The Attempt at a Solution



I got the i and j components and put them together as follows.

F3= (346.41i -200j) - (180i + 240j) - (500i)
F3 = -334i - 440j

this answer is incorrect as it would mean that cable F3 is going through the wall? Any help would be appreciated, thanks.
 

Answers and Replies

  • #2
rude man
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You sure you got the problem right?
 
  • #3
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You sure you got the problem right?
where do you think i went wrong? I even checked it back against the original Fr = F1 + F2 + F3 and it comes up with the correct Fr.

Am i looking at the problem in the wrong way?
 
  • #4
NascentOxygen
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Perhaps you copied that 400 value wrong? Maybe it should be 800 or so?
 
  • #5
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Perhaps you copied that 400 value wrong?
i was thinking this as well, i've checked my figures though and re-checked the final answer against the resultant force and it seems correct but it doesnt fit with what the photo shows
 
  • #6
PhanthomJay
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I'd chuck this problem as far as I could throw it and find another that makes more sense.
 
  • #7
rude man
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I'd chuck this problem as far as I could throw it and find another that makes more sense.
I second that motion.
 
  • #8
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There doesn't appear to be anything wrong with this problem apart from a terrible drawing...
 
  • #9
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I'd chuck this problem as far as I could throw it and find another that makes more sense.
I second that motion.
There doesn't appear to be anything wrong with this problem apart from a terrible drawing...
I talked to my lecturer and she said that the problem is either it is drawn wrong or the figures that were given in the question are wrong because there is nothing wrong with how i worked it out lol. Spent ages trying to figure out where I went wrong.

Thanks for the help everyone as well!!
 
  • #10
NascentOxygen
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I talked to my lecturer and she said that the problem is either it is drawn wrong or the figures that were given in the question are wrong because there is nothing wrong with how i worked it out lol. Spent ages trying to figure out where I went wrong!
Thanks for getting back, Popa91.
 
  • #11
nvn
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Popa91: Theoretically speaking, there is nothing wrong with the given problem, nor diagram. You worked the problem correctly, and your answer in post 1 is correct. We can imagine ways in which the given problem is possible.
 

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