Question

Two vectors, both equal in magnitude, have their resultant equal in magnitude to any of the two vectors. Find the angle between the vectors.

• A. ${60}^{\circ }$
• B. ${75}^{\circ }$
• C. ${90}^{\circ }$
• D. ${120}^{\circ }$

Answer 1

The correct option is D ${120}^{\circ }$

Let $\theta$ be the angle between the two vectors
$\therefore$ $A^2=A^2+A^2+2AA\cos \theta$
which gives, $\cos \theta =-\frac{1}{2}$
$\theta ={120}^{\circ }$