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  • If  <img alt="\left | \vec{A}+\vec{B} \right |=\left | \vec{A} \right |=\left | \vec{B} \right |" src="http://entrancecorner.oncodecogs.com/gif.latex?%5Cleft%20%7C%20%5Cvec%7BA%7D&plu

If  \left | \vec{A}+\vec{B} \right |=\left | \vec{A} \right |=\left | \vec{B} \right | , then angle between \vec{A} \,and\: \vec{B} is (in degrees)

Option: 1

120


Option: 2

60


Option: 3

90


Option: 4

0


Answers (1)

best_answer

As we learned

 From  the triangle law of vector addition,

 \left | \vec{A}+\vec{B} \right |=\sqrt{A^2+B^2+2AB\cos \theta }

                   =\sqrt{A^2+A^2+2A^2\cos \theta }   \left | \vec A +\vec B\right |^2=\left | \vec A \right |^2=2A^2+2A^2cos \theta

\\ \Rightarrow \cos{\theta}=-\frac{1}{2} \\ \therefore \theta=120\degree

Posted by

Divya Prakash Singh

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