4. (10 points) Denote by r(t) and v(t) the position and velocity vectors of a particle at time t. Assume that r(0) = (1, 0, 1) and v(t) = (cost, sint, vt + 2). (a) (5 points) Find r(t). (b) (5 points) Find the length of the curve r(t) over the interval 0