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Astrum

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## Homework Statement

A particle moves with constant speed v around a circle of radius b. Find the velocity vector in polar coordinates using an origin lying

**on**the circle.

https://www.desmos.com/calculator/maj7t9ple1

Imagine the

**r**starts at (0,0).

## Homework Equations

[tex]\frac{d\vec{r}}{dt}[/tex] = [tex]\dot{r}\hat{r}+r\dot{\theta}\hat{\theta}[/tex]

## The Attempt at a Solution

We can make a triangle connecting the origin to the center of the circle, to a point where the particle is. the hypotenuse is

**r**

I assume I need to find the rate of change of

**r**, right? So, could I just do

[itex]r=b/cos(\theta)[/itex] [tex]\frac{dr}{dt}=\frac{dr}{d \theta}\frac{d \theta}{dt}[/tex]

[tex]\frac{dr}{dt}=b\frac{tan(\theta)}{cos(\theta)} \frac{d\theta}{dt}[/tex]

My book doesn't do this, which leads me to believe I've made some horrible mistake.

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