Three runners A, B, and C sprint along a straight track. For the first 6 s of the race the velocity–time representation for each runner is a straight-line segment, summarized below:
• Runner A starts from rest and the magnitude of velocity increases linearly to 6m/s at t=6s.
• Runner B maintains a constant velocity of 3m/s.
• Runner C starts with a velocity of 6m/s and its magnitude decreases linearly to 0m/s at t=6s.
All three runners begin at the same starting line, and the positive direction is toward the finish line.
(a) Rank the runners by their displacement from the starting line at t=6s, from greatest positive displacement to least, without performing numerical calculations.
(b) Determine which runner, if any, experiences a negative acceleration during the interval, and justify your answer based on the features of the velocity–time description.
(c) Sketch qualitatively an acceleration–time graph for Runner A on axes with properly labeled quantities. No numerical scales are required; indicate only the sign of the acceleration.
(d) The runners continue beyond t=6s. Without additional information, is it possible for Runner C to cross back over the starting line moving in the negative direction? Explain your reasoning qualitatively.