10. A bullet train travels along a straight train track so that its positive relative to Station O is given by: s(t) = t3 - 15t2 + 48t - 100, t 2 0 where time is in seconds and distance is in metres. a Find the velocity function at time t. [1A] b) Find the acceleration function at time t. [1A] c) Did the train change direction at any time within the first 10 seconds? Justify with calculation. [1A]