# NEET Questions Solved

PMT - 1999

Two forces with equal magnitudes F act on a body and the magnitude of the resultant force is F/3. The angle between the two forces is

(1) ${\mathrm{cos}}^{-1}\left(-\frac{17}{18}\right)$

(2) ${\mathrm{cos}}^{-1}\left(-\frac{1}{3}\right)$

(3) ${\mathrm{cos}}^{-1}\left(\frac{2}{3}\right)$

(4) ${\mathrm{cos}}^{-1}\left(\frac{8}{9}\right)$

(1) ${F}_{{}_{net}}^{2}={F}_{1}^{2}+{F}_{2}^{2}+2{F}_{1}{F}_{2}\mathrm{cos}\theta$

${\left(\frac{F}{3}\right)}^{2}={F}^{2}+{F}^{2}+2{F}^{2}\mathrm{cos}\theta$

$\mathrm{cos}\theta =\left(-\frac{17}{18}\right)$

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