An object starts at x = 0 m on a straight track. It travels 72 m in the positive direction in 18 s, remains still for 6 s, then travels 24 m in the negative direction in 12 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.

Question

Accepted Answer

Final position 48 m; distance 96 m; average speed 2.6667 m/s; average velocity 1.3333 m/s. Choose the stated positive track direction and preserve the signs. The final coordinate is 72 − 24 = 48 m, which is also the displacement because the starting coordinate is zero. Distance counts every travelled section without cancellation: 72 + 24 = 96 m. The stationary stage adds no distance but still occupies time. The complete elapsed time is 18 + 6 + 12 = 36 s. Therefore average speed is total distance divided by this time: 96/36 = 2.6667 m/s. Average velocity uses signed displacement instead: 48/36 = 1.3333 m/s. Its sign identifies the overall displacement direction, not every direction used along the route. The individual moving speeds are 4 and 2 m/s. Neither alone includes both travel stages and the pause, so neither is automatically the correct whole-journey average.

Warehouse scanning pause

What a complete response should do

How did this one feel?