Hey guys, got a polar coordinates question Im stuck on.

A particle is moving with constant velocity along the line . Describe in polar coordinates.

I worked out that and differentiating that shouldnt be too much of a problem but Im stuck with theta

Ive got

but Im guessing I cant just differentiate this using , since theres in there instead of .

I worked through it using and ended up with

but I'm not sure how to get this in terms of t or if I even worked it out right. Also Im hoping I can replace my s in the formulas with , I think I only need the magnitude for polar coords?

any help would be appreciated greatly!