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Finding the Resultant force 
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#1
Oct210, 01:18 AM

P: 98

Ok so I have something like this...not drawn to scale
http://i53.tinypic.com/303l5k6.gif I can see that with the law of cos I can get 49N However...with this other method where you set Sum of F=0 With sqrt(Fx^2+Fy^2)=R sqrt((40*cos(20)+20*cos(30))^2+(40*sin(20)20*sin(30))^2) I get 55N Is there soemthing wrong? I'm pretty sure the first answer is correct...but I don't know why this one isnt... 


#2
Oct210, 02:51 AM

P: 1,261

The second one looks right, so I'm guessing the first is wrong.... what do you mean using the law of cos?
I think the best way is to just break down each force vector into its x and y components; add those to find the resultant, then use the Pythagorean theorem to find the magnitude of the resultant (that's effectively what you did with your second method). 


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