A body moves on a coordinate line such that it has a position s=f(t)=- a. Find the body's displacement and average velocity for the given time interval. b. Find the body's speed and acceleration at the endpoints of the interval. c. When, if ever, during the interval does the body change direction? The body's displacement for the given time interval is (Type an integer or a simplified fraction.) 2 on the interval 1 sts 2, with s in meters and t in seconds. m.