
#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: 1,262

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). 


Register to reply 
Related Discussions  
electrostatics. finding the resultant force!  Introductory Physics Homework  1  
help finding resultant force and angle  Introductory Physics Homework  0  
Finding resultant force/vector help?  Introductory Physics Homework  1  
Finding resultant force  Introductory Physics Homework  9  
Finding the resultant force  Introductory Physics Homework  7 