# Perpendicular position vector and velocity?

1. Feb 3, 2005

### quiksilver

I have been struggling with this question for a little while now and after drawing pictures and such I just cannot think of a situation in which this is possible. I was wondering if somebody with a little bit more physics knowledge could enlighten me ? Here it is:

"Describe a situation in which the velocity of a particle is always perpendicular to the particle's position vector."

2. Feb 3, 2005

### Tide

How about a satellite moving in a circular orbit around a planet? Or an electron moving in a uniform magnetic field?

3. Feb 3, 2005

### MathStudent

In uniform cirucular motion, the velocity vector is tangent to the circle at each point. The position vector is a vector from the origin to the point corresponding to its position... thus if your circle has its center at the origin, then this would be an example of what you described.

4. Feb 4, 2005

### quiksilver

Tangent is perpendicular to a point on a circle...a real life example like a satellite orbiting a planet.

My problem is that I havent learned about this yet, this is a pre-class question...so I was not thinking in circular motion I was stuck in linear thought so all of my situations werent coming out right...thanks for the help

5. Feb 4, 2005

### arildno

Go into the particle's rest frame, and position it wherever you'd like there.
Since the velocity is the zero vector, the velocity vector is perpendicular to the position vector..