A cheetah is traveling across the African countryside, initially moving at a constant velocity of 9.0 m/s. It sees a gazelle at t = 0 seconds and begins to accelerate in a straight line. At t = 4.0 seconds it has a velocity of 23 m/s and then continues to move at this constant velocity. At t = 5.0 seconds, the cheetah is standing still, having knocked over the gazelle. (a) What is the average acceleration of the cheetah from t = 0 to t = 4.0 seconds? (b) What is the average acceleration of the cheetah from t = 0 to t = 5.0 seconds?