a couple of questions

[jlmac2001]

1. Is every quantity that has three components in three dimensions a vector? From the definition of a vector I think it is. If it isn't, can you give me an example?

2. How can you tell if the projection of a force vector F along the velocity vector v of a particle is a scalar?

[himanshu121]

It would be possible if it obeys vector law of addition
Consider a current flowing through junction which is attached to three dimension network, it will have magnitude in 3 direction.
But definitely current is a scalar quantity

Projection along v will be fcos(theta)

Now F.v=Fcos(theta)*v Therefore

Fcos(theta)= (F.v)/v which is clearly scalar