A) \[{{\cos }^{-1}}\left( -\frac{17}{18} \right)\]
B) \[{{\cos }^{-1}}\left( -\frac{1}{3} \right)\]
C) \[{{\cos }^{-1}}\left( \frac{2}{3} \right)\]
D) \[{{\cos }^{-1}}\left( \frac{8}{9} \right)\]
Correct Answer: A
Solution :
\[F_{_{net}}^{2}=F_{1}^{2}+F_{2}^{2}+2{{F}_{1}}{{F}_{2}}\cos \theta \] Þ \[{{\left( \frac{F}{3} \right)}^{2}}\]\[={{F}^{2}}+{{F}^{2}}+2{{F}^{2}}\cos \theta \] Þ \[\cos \theta =\left( -\frac{17}{18} \right)\]
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