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Position-Time Graphs:
Position versus time graphs represent changes that occur in an object's position with respect to time. The slope of the line is the velocity (change in position divided by the change in time) of the object.
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The slope of the line on a position-time graph reveals information about an object's velocity. The slope is the velocity; so "as the slope goes, so goes the velocity." If the slope is 0 (as for a horizontal line), then the velocity is 0. If the slope is large, then the velocity is large. If the slope is small, then the velocity is small. If the slope is constant (as for a straight line), then the velocity is constant. If the slope is changing (as for a curved line), then the velocity is changing. If the slope is positive (sloping upward), then the velocity is positive. If the slope is negative (sloping downward), then the velocity is negative. As the slope goes, so goes the velocity.
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This question asks you to identify all time intervals during which the velocity is both nonzero and constant. A zero velocity corresponds to a line with 0 slope - i.e., a horizontal line. So you need to be looking for a line that is NOT horizontal. A constant velocity corresponds to an object with a constant slope. So you need to be looking for a line which is straight and diagonal - i.e., not horizontal and not curved.
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