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Finding resultant force

by Saladsamurai
Tags: force, resultant
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Saladsamurai
#1
Dec18-07, 06:33 PM
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1. The problem statement, all variables and given/known data
Okay, I am only allowed to use law of cosines and sones to find the resultant force F_r

I am having a hell of a time finding a usable angle after drawing my parellelogram..so obviously I am in need of sleep.

What am I missing here? (pic is clickable)



Casey
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Saladsamurai
#2
Dec18-07, 06:45 PM
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I know I need to isolate a triangle, but I really suck at similar triangles when they are not necessarily right triangles.
Doc Al
#3
Dec18-07, 06:46 PM
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Draw yourself a diagram where you add the vectors (head to tail addition). The two vectors are the two sides of a triangle. You should be able to identify the angle between them and apply the law of cosines to find the third side of the triangle, which will be the resultant.

G01
#4
Dec18-07, 06:47 PM
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Finding resultant force

The 120 degree angle should be the angle corresponding to your resultant vector in the triangle. For the other angles:

HINT: What is the angle between the 80lb force and the -x axis? Does this help you find another angle in your parallelogram?
Saladsamurai
#5
Dec18-07, 06:48 PM
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Is the angle between them by any chance 60 degrees? In the parellepgram 2(120)=240 leaving 120/2 to give me four angles that add to 360
Doc Al
#6
Dec18-07, 06:50 PM
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Quote Quote by Saladsamurai View Post
Is the angle between them by any chance 60 degrees?
Yes. (Assuming you're talking about the triangle I referred to.)
Saladsamurai
#7
Dec18-07, 06:51 PM
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I'll be back in 20 minutes. All of the theological students just showed up at StarBucks and I can't take their banter.....I'm going home.

Casey

Quote Quote by Doc Al View Post
Yes. (Assuming you're talking about the triangle I referred to.)
Angle between 60 and 80 with tail of 60 at tip of 80.
Doc Al
#8
Dec18-07, 06:53 PM
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Run for it, man!
Saladsamurai
#9
Dec18-07, 07:43 PM
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I made it home!

Thanks Doc and G01! I am taking this Statics course over X-mass break :points gun into mouth and fake blows brains out:

So is the general approach to these to use the fact that vectors can be moved around to redraw the scenario in a manner that helps to generate more information from the given info?

Casey
Doc Al
#10
Dec18-07, 07:47 PM
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Yes. When adding vectors, you can move them around at will as long as you keep the magnitude and direction the same.


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