Final answer:
The shortened hose can be used as a level area beyond the marble's acceleration on the slope to measure displacement and elapsed time.
Step-by-step explanation:
The hose that has been shortened to 40' can be used as a level area beyond the accelerating object, which in this case is the marble. By placing the level area beyond the marble's acceleration on the slope, you can measure the displacement of the marble and the elapsed time using a stopwatch.