Vector calculus on particle movement

Hello,

I'm currently working on a question which is about a particle moving across along a line. The particle is moving along the line log (x) at a constant speed of one. When t = 0, the particle is at point (1,0). I have to find a) the velocity vector and b) the acceleration vector at (1,0).

I've start off by making . To find the velocity vector, I must differentiate . So: . This is where I get stuck. I know that the speed of the particle is 1 at any time t. So . I feel I need to find the value x'(t). Is this right? If so, how do I find it?

Thanks for your help.