17. If a particle of mass \( m \) resting at the top of a fixed smooth hemisphere of radius \( R \) is displaced, the the angle with vertical at which it looses contact with the surface is
(A) \( \tan ^{-1}\left(\frac{1}{3}\right) \)
(B) \( \cos ^{-1}\left(\frac{1}{3}\right) \)
(C) \( \tan ^{-1}\left(\frac{2}{3}\right) \)
(D) \( \cos ^{-1}\left(\frac{2}{3}\right) \)