When analyzing a displacement-time graph, the velocity can be determined by examining the slope of the graph. If you're looking at the portion of the graph that occurs below the horizontal axis (the time axis), it often indicates that the object is moving in the negative direction relative to the chosen displacement reference point.
Here's what you can infer from that part of the graph:
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Negative Displacement: If the graph shows negative values of displacement (below the horizon), it generally indicates that the object is positioned in a negative direction from the reference point.
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Velocity Calculation: The velocity at any point on the graph is calculated as the slope of the line (change in displacement/change in time). A slope that is negative indicates that the velocity is negative, suggesting that the object is moving in the opposite direction to what has been defined as positive.
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Trends on the Graph: If the slope is steep, the velocity (in the negative direction) is high. If the slope is shallow, the object's speed is lower. If the line is horizontal (slope = 0), the object is at rest.
In summary, when calculating velocity from a displacement-time graph, if you find the graph below the horizontal axis, you can conclude that the object is moving in a negative direction (assuming conventional definitions of displacement), and the velocity will also be negative, reflecting this motion.