A) \[20{}^\circ \]
B) \[135{}^\circ \]
C) \[120{}^\circ \]
D) \[45{}^\circ \]
Correct Answer: C
Solution :
Given : \[\vec{A}=\vec{B}=\vec{R}\] Resultant, \[{{R}^{2}}={{A}^{2}}+{{B}^{2}}+2AB\cos \theta \] \[{{A}^{2}}={{A}^{2}}+{{A}^{2}}+2AA\cos \theta \] \[1=1+1+2\cos \theta \] \[2\cos \theta =1-2=-1\] \[\cos \theta =-\frac{1}{2}=\cos {{120}^{o}}\] \[\theta ={{120}^{o}}\]
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