Question
If $|\,\vec A + \vec B\,|\, = \,|\,\vec A\,| + |\,\vec B\,|$, then angle between $\vec A$ and $\vec B$ will be ....... $^o$
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Answer
(c) Resultant of two vectors $\overrightarrow A $ and $\overrightarrow B $ can be given by
$\overrightarrow R = \overrightarrow A + \overrightarrow B $
$|\overrightarrow R |\, = \,|\overrightarrow A + \overrightarrow B |\, = \sqrt {{A^2} + {B^2} + 2AB\cos \theta } $
If $\theta = 0^\circ $ then $|\overrightarrow R |\, = A + B$$ = \,|\overrightarrow A | + |\overrightarrow B |$
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