Elevator Design - Rack and Pinion Cascaded - 772

[Ether]

Originally Posted by akoscielski3

I'm going to believe you in this because you are an engineer and I am just a student, but I have a hard time wrapping my head around the fact that I should include the weight of the Assembly that doesn't move.

If you want to use the weight of only the moving piece, then you can do that... but the distance you would use is the distance the moving piece moves, not the distance the center of mass of the assembly (including the non-moving portions) moves.

edit:

See attached sketch. On the left is a "system" consisting of a 10 lb red block and a 10 lb blue block. The center of mass of this system is located at the gray circle between them in the middle.

I now lift the blue block 2 feet. The center of mass of the system is now 1 foot higher than it was. I can calculate the work either way:

1) work = weight of system * distance I changed the center of mass of the system = 20 lbs * 1 ft = 20 ft-lbs.

2) work = weight of the piece I lifted * distance I lifted that piece = 10 lbs * 2 ft = 20 ft-lbs.