# Homework Help: Confused about uniform circular motion (and it's velocity vector)

1. Feb 18, 2010

### Tobias101

Sorry if this is the wrong (sub)forum!

I need some help to understand how to express the following:

The velocity vector

When this is given:

Omega
radius

Both in magnitudes. I want to obtain an expression for the velocity vector when the angle theta (radians/s) is changed. That is, when i know the position of the particle:

(x,y) = r*(cos(theta),sin(theta)) Note: center is at (0,0)

I know the velocity vector is tangent to the point on the circle at any given time, and that it can be determined via the cross-product between the vectors omega and r, that is:

V = Omega X r

But how do i convert from magnitudes to vector form?? - it's very simple, i'm sure of it, but i cannot see anything in my book in calculus...

Any help appreciated - i hope i made myself clear

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