8. A person throws a rock directly upward with initial height 4 ft and initial speed 60 ft/s. On Earth, acceleration due to gravity is 32 ft/s2 (or 9.8 m/s2) downward. a) We already know the rock's acceleration. Use this and your knowledge of derivatives to express the rock's velocity (in ft/s) and the rock's height (in feet) as functions of time. b) After how many seconds does the rock hit the ground? c ) What is the rock's impact velocity? d) How far does the rock travel during its flight