the position vector of a point which moves in the x-y plane is given by:
r = (- 0.2 t4 + 1.8 t3 + 1.1 t2) i + (- 0.4 t4 - 1.2 t) j
where r is in meters and t is in seconds. Determine the angle between the velocity v and the acceleration a when t = 1.7 s