A distance–time graph shows a straight line with a slope of 3 m/s. What is the speed of the object, and how would you describe its motion?

• A. Speed is 3 m/s; motion is constant speed in a straight line.
• B. Motion is constant speed in a straight line; speed is 3 m/s.
• C. Speed is 0; motion is stopped.
• D. Speed is 6 m/s; motion is in a circular path.

Answer: (A)

On a distance–time graph, the slope tells you the speed, and a straight line means the speed isn’t changing over time. The line has a positive slope of 3 m/s, so the speed is 3 m/s. Because the line is straight, the motion is at a constant speed in a straight line—moving in one direction without speeding up or slowing down.

This matches the statement that describes both the speed and the constant, straight-line motion in a concise way. If the slope were zero, the object would be at rest; a curved line would indicate changing speed or direction, and a different slope would mean a different speed.