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Silly Parallelogram Question 
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#1
Jun2412, 02:03 PM

P: 24

1. The problem statement, all variables and given/known data
Determine resultanat force of vectors P (40N) and Q (60N). P is 20 degrees from reference plane and Q is 45 degrees from reference plane. 2. Relevant equations When using the parallelogram rule, should you always start with the lowest angle vector? (like in the bottom diagram of the attached image) 3. The attempt at a solution I solved the question using the parallelogram in two different ways and ended up with different answers. Is there a right way to do this? Solution 1: P vector, then Q vector with resultant vector starting at tail of P to tip of Q. Law of Cosines yields, R = 97.726N Law of Sines yields, Angle A = ∠15.039 alpha = ∠20 + ∠15.039 = ∠35.04 Solution 2: Q vector, then P vector with resultant vector starting at tail of Q to tip of P. Law of Cosines yields, R = 98.542N Law of Sines yields, A = ∠7.9803 alpha = ∠45  ∠7.9803 = ∠37 Diagram attached. 


#2
Jun2412, 02:44 PM

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#3
Jun2512, 10:50 AM

P: 24

Sorry, I used the wrong value for the angle in cosine. It should have been 155 and I used 160. This should be correct, the textbook I'm working from has the same as their answer. It could be wrong but I doubt it.
Here's the complete walkthrough of the problem: R^2=〖60〗^2+〖40〗^22*40*60cos(155) R = 97.726N sin(A)/40 = sin(155)/97.726 A = 9.9612 alpha = 35.039 


#4
Jun2512, 10:53 AM

P: 24

Silly Parallelogram Question
I'm not sure if the diagram I gave is showing up but it should have everything you need on there. No worries guys, it was a stupid mistake.



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