A particle moves so that its position vector varies with time as r→=Acos⁡ωti^+Asin⁡ωtj^. The initial velocity of the particle is

Substituting r→=(Acos⁡ωti^+Asin⁡ωtj^) in v→=dr→dt we have v→=Addt(cos⁡ωt)i^+Addt(sin⁡ωt)j^=−Aωsin⁡ωti^+Aωcos⁡ωtj^ At  t=0,v=−Aωsin⁡0i^+Aωcos⁡0j^=Aωj^