Q. Given $\overrightarrow{R} = \overrightarrow{A} + \overrightarrow{B}$ and $R = A = B$. The angle between $\overrightarrow{A}\ and\overrightarrow{\ B}$ is
A) 60${^\circ}$
B) 90${^\circ}$
C) 120${^\circ}$
D) 180${^\circ}$
Explanation
(c) $R^{2} = R^{2} + R^{2} + 2R^{2}\ cos\theta$ or $R^{2} = 2R^{2} + {2R}^{2}cos\theta$
$\frac{1}{2} = 1 + cos\theta$ or $cos\theta = - \frac{1}{2}$ or $\theta = 120{^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.