# Uniform circular motion and coordinate system

1. Jun 21, 2008

### ace123

2. In the figure below the particle P is in uniform circular motion. The motion is centered on the origin of an xy coordinate system.
(a) At what values of $$\vartheta$$ is the vertical component r$$_{y}$$ of the position vector greatest in magnitude?
(b) At what values of $$\vartheta$$ is the vertical component v$$_{y}$$ of the particle’s velocity greatest in magnitude?
(c) At what values of $$\vartheta$$ is the vertical component a$$_{y}$$ of the particle’s acceleration greatest in magnitude?

a. How can radius have a vertical component? It's just a distance or would it be a displacement?

b. Isn't velocity always tangential to the circle so how would there be a y component? Or does he just mean when it points in the y direction like at zero and 180 degrees?

c. Would it be 90 degrees and 270 because it only has a vertical component?

Any help would be appreciated

2. Jun 21, 2008

### ace123

The figure is in my gravitational force post. I don't know how to move it. It's question 2.

3. Jun 21, 2008

### G01

You have the basic idea correct. The magnitude of the y component of each vector is greatest when the whole vector lies along the y-axis. So, your answers to b) and c) are correct.

For part a) you are working with a position vector, not just a distance. The radial position vector points outward from the origin toward the object. Can you answer part a) now?

4. Jun 21, 2008

### ace123

Yea I can answer it now. I just didn't know it was a vector thought it was just a scalar. Shouldn't it just be at 90 degrees and 270 again?

5. Jun 21, 2008

### G01

You got it.

6. Jun 21, 2008

### ace123

Thanks for the help