Q. Two forces, each of magnitude $F$, have a resultant of the same magnitude $F$. The angle between the two forces is
A) 45${^\circ}$
B) 120${^\circ}$
C) 150${^\circ}$
D) 180${^\circ}$
Explanation
(b) $F^{2} = F^{2} + F^{2} + 2F^{2}cos\theta$
or $F^{2} = 2F^{2}(1 + cos\theta)$
or $1 + cos\theta = \frac{1}{2}$
or $cos\theta = - \frac{1}{2}$ or $\theta = 120{^\circ}$
$\therefore\ \cos 120{^\circ} = - \frac{1}{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.