An object moves along a straight track. A position–time graph for the object is described below. From t = 0 s to t = 2 s, the graph is a straight line that rises uniformly from x = 0 m to x = 4 m. From t = 2 s to t = 4 s, the graph is a smooth curve that continues to rise from x = 4 m to x = 8 m but with progressively smaller slope; at t = 4 s the curve becomes horizontal. From t = 4 s to t = 6 s, the graph is a horizontal line at x = 8 m. Three labeled points are indicated: point A at t = 1 s, point B at t = 3 s, and point C at t = 5 s.
(a) Describe the direction of motion (forward, backward, or at rest) of the object at each of the three labeled points. Explain how you know.
(b) Rank the magnitudes of the instantaneous velocities at points A, B, and C from greatest to least. Justify your ranking.
(c) Is the object's acceleration between t = 2 s and t = 4 s positive, negative, or zero? Provide reasoning based solely on the given graph.