(kinematics) Is it to derive into radial and transverse components?

[fociboy]

Homework Statement

A wire OA connects the collar A and a reel located at O as shown in the picture. Knowing that the collar moves to the right at a constant speed v0, determine θ'' (the 2nd-order-derivative of θ) in term of v0, b and θ.
http://www.freeimagehosting.net/uploads/3cad8b54c6.jpg

Is it to derive into radial and transverse components?
I can't figure out the unit vector e _θ and e_r. How can we set up it?

 

[tiny-tim]

Knowing that the collar moves to the right at a constant speed v0, determine θ'' (the 2nd-order-derivative of θ) in term of v0, b and θ.

Hi fociboy!

You know the horizontal speed is constant, so use x and y coordinates, and x' = v₀, y' = 0, and rewrite in terms of r' and θ'.