An object starts at x = 0 m on a straight track. It travels 90 m in the positive direction in 45 s, remains still for 15 s, then travels 30 m in the negative direction in 30 s. Each moving stage has constant speed and direction changes take negligible time. Find its final position, total distance, average speed and average velocity for the whole journey. Explain why a moving-stage speed cannot replace the whole-journey average.

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Final position 60 m; distance 120 m; average speed 1.3333 m/s; average velocity 0.6667 m/s. Choose the stated positive track direction and preserve the signs. The final coordinate is 90 − 30 = 60 m, which is also the displacement because the starting coordinate is zero. Distance counts every travelled section without cancellation: 90 + 30 = 120 m. The stationary stage adds no distance but still occupies time. The complete elapsed time is 45 + 15 + 30 = 90 s. Therefore average speed is total distance divided by this time: 120/90 = 1.3333 m/s. Average velocity uses signed displacement instead: 60/90 = 0.6667 m/s. Its sign identifies the overall displacement direction, not every direction used along the route. The individual moving speeds are 2 and 1 m/s. Neither alone includes both travel stages and the pause, so neither is automatically the correct whole-journey average.

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