Originally Posted by

**youngb11** A car's position is given by $\displaystyle d(t)=2t^3-24t^2+78t-56$, find when it is speeding up and speeding down.

I'm a little confused if it means the acceleration (2nd derivative) or velocity (1st derivative). I'd have thought acceleration, but the 2nd derivative is only positive when $\displaystyle t>4$, but when looking at its graph (http://www.wolframalpha.com/input/?i=2x^3-24x^2%2B78x-56), you' assume it was speeding up after it hit its maximum value until the inflection point.

Was I right for thinking it speeds up after it hit the max/min?