Relative motion problem (with picture)

[unknownman]

Homework Statement

http://imgur.com/EcjIa

Homework Equations

I already got the first part (v_b/a) i need to find r dot and theta dot

The Attempt at a Solution

well i got v_b/a. for r I was thinking of using sqrt(y^2 +x^2) at the r and taking derivatives of that. i don't quite understand polar coordinates

 

[DaveC426913]

You need to show your attempt at the solution. WE cannot give you help until you have shown your own attempts.