Pulley Hoist Free Body Diagram

1. Mar 5, 2013

SGT_in_WI

Hi All,

I am an old dog, and rusty propeller head. I am having the most difficult time figuring out the forces on a pulley system I am working on. Can someone please review my sketch and tell me if I am even close. I would accept any suggestions and direction.

Much Obliged
-Steve

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2. Mar 5, 2013

Staff: Mentor

How can you support W/2 with two strings of W/8 tension (in addition, they have some angle between them!)
In addition, what happens to the end of the string (right side)? I think it should help to support the weight, too.

W/8 is a force, the tangent of a force is not well-defined.

3. Mar 5, 2013

SGT_in_WI

Yes, I knew my W/2 did not add up correctly with 2 - W/8 loads. That is really where I need help.

W/2 is a pulley at each end of the W
The angle is not counted at this time to avoid further confusion.
The end of the string is lifting W
I drew the tangent of middle pulleys for reference. The load on them will not affect my system I am building. I can calculate the load after I correctly figure out the force multiplier of my pulleys.

I hope I helped clear some up your questions.

4. Mar 5, 2013

Staff: Mentor

The end of the string is lifting the same as all other parts. If we approximate that those string elements are vertical, we have 5 times the string tension holding that weight W, so string tension is W/5.

5. Mar 5, 2013

SGT_in_WI

Thank you,

So that I have more understanding...

Is the weight only carried by the string between pulleys B-C, C-D, G-H, H-I , I-to end?

Also; Is my W/2 at pulleys C and H correct?

Do I substitute W/5 for where I have W/8 throughout the string?

-Steve

6. Mar 6, 2013

Staff: Mentor

As the other parts are not connected to the weight... sure.
No, as you did not consider the end here.
Right

7. Mar 6, 2013

SGT_in_WI

Thank you !

I believe I have all that I need.

Peace.