Phy simple one

ya......
just as the "work done = F x s" which is valid only when both force and displacement are in the same direction. ....u may think of that power = F x s/t
actually, the multiplication of 2 vector quantity, like force and displacement is represented by " IFI x IsI x cosθ" where θ is the angle between 2 vectors, so that the dircetion multiplication of the quantitive value of the vector F and v in calculation of power is only valid when they are parallel with each other. otherwise the angle between should be taken into calculation.