= The acceleration of a particle moving only on a horizontal xy plane is given by a squared and t is in seconds. At t = 0, the position vector 7 (18.0m) + (43.0m) vector = (7.50m/s)i + (3.10m/s). At t = 5.10 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? 5ti +61), where a is in meters per second- locates the paticle, which then has the velocity