The acceleration of a particle moving only on a horizontal xy plane is given by a = 211 + 31, where a is in meters per second- squared and t is in seconds. At t = 0, the position vector = (16.0m) + (40.0m), locates the paticle, which then has the velocity vector = (7.60m/s) + (2.20m/s)). At t = 4.00 s, what are (a) its position vector in unit-vector notation and (b) the angle between its direction of travel and the positive direction of the x axis? (a) Number i (b) Number i Units Units