How Do You Calculate the Resultant Force and Its Direction from Two Vectors?

[freespirit]

My problem is to determine the magnitude and direction of the resultant force FR=F1+F2 and it's direction, measured counterclockwise from the positive x direction.

f1=250 lb @ 60 degrees from x
f2= 375 lb @ -45 degrees from x

Ok I got the magnitude by doing this:
(360-2(255))/2=-75 degrees

fr=sqroot of (250^2+375^2-2(250)(375)cos(75)
fr=393.188~ 393

then I got the angle by this:
375/sin x = 393.188/sin 75
x=67.1088
how do i get the resultant angle, what do I need to add to the 67 degrees?




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[himanshu121]

U have ur replies at Homework Section where the above pro should be

 

[mathman]

The easiest way to do it is by computing the x and y components of F1 and F2, add them respectively to get the x and y components of FR, and compute the magnitude and directions from these. It is a simple analytic geometry problem.