What is the angle between two forces of equal magnitude, F_aFa and F_bFb, when the magnitude of their resultant is also equal to the magnitude of either of these forces?

1 Answer
Jul 28, 2016

theta=(2pi)/3θ=2π3

Explanation:

Let the angle between F_a and F_bFaandFb be thetaθ and their resultant is F_rFr So

F_r^2=F_a^2+F_b^2+2F_aF_bcosthetaF2r=F2a+F2b+2FaFbcosθ
Now by the given condition
let F_a=F_b=F_r=FFa=Fb=Fr=F

So

F^2=F^2+F^2+2F^2costhetaF2=F2+F2+2F2cosθ

=>costheta=-1/2=cos(2pi/3)cosθ=12=cos(2π3)

:.theta=(2pi)/3