2. The position of an object moving along a line at any time t 2 0 is given by the function s(t) = t3 9t2 + 18 , where s is measured in feet and t is measured in seconds. . Find the velocity of the particle at t = 4. . Find the acceleration of the particle at t = 4. . Was the speed of the particle increasing or decreasing at t = 4 ? Justify your answer. . For t > 0, find the acceleration when the particle changes direction