So this looks really easy, but I can't get the right answer. It asks you to find the minimum acceleration from the graph: http://s22.postimg.org/f5dutd5ap/pic.png. This is of course the point where the slope is the smallest, and this is from t = 3-4 s or t = 4-5 s, depending on whether you want to find the positive/negative acceleration. Either way it's about (57 m/s - 55 m/s)/1 s, 2 m/s2. It doesn't accept this answer or 1, 3, 4, 5 or the negatives of those. I'm not sure what's going on, this is pretty basic. There's no way the lowest acceleration is greater than 5, and it is most obviously based on the graph about 2 or 3.