The position function of a particle in rectilinear motion is given by s(t) = 2t^3 - 21t^2 + 60t + 3 for t ≥ 0. find the position and acceleration of the particle at the instant when the particle reverses direction. include units in your answer.
so i've already gotten the first derivative(6t^2-42t+60) and set it to 0. this resulted in t=5 and t=2. i then took the second derivative(12t-42) and plugged in t for acceleration. where do i go from here?