A particle is moving along the circle $x^2 + y^2 = a^2$ in anti clock wise direction. The $x-y$ plane is a rough horizontal stationary surface. At the point $(a\, cos\theta , a\, sin\theta )$, the unit vector in the direction of friction on the particle is:
  • A$\cos \theta \,\hat i + \sin \theta \,\hat j$
  • B$ - \left( {\cos \theta \,\hat i + \sin \theta \,\hat j} \right)$
  • C$\sin \theta \,\hat i - \cos \theta \,\hat j$
  • D$\cos \theta \,\hat i - \sin \theta \,\hat j$
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