# Determining Force and Directions on Truss with Pulley

• Engineering
• trusshelp148
In summary, the cable has 2000 kg-mass in tension, with two compression forces going down the two links that meet at each node. Pivots A and B are each loaded with (19.6 x 2) kN, and can be visualized by calculating the moments about them.

#### trusshelp148

Homework Statement
I am struggling to figure out if I did this problem correctly. I am supposed to determine the forces acting on all of the links, as well as whether they are in tension or compression. There is an image included below.
Relevant Equations
∑Fx=0
∑Fy=0
∑M=0
So far I have used methods of joints to determine the forces at point E, D, and C. However, there is also a pulley attached to point D and E which I included in the sum of forces, but I'm not sure if that's the correct way to apply them. Every force I've calculated so far has also been in tension, which does not seem right. I'm also unsure of how to calculate the reactions at A and B with the pulley involved. Any help would be much appreciated.

#### Attachments

• diagram.png
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• Point E.png
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• Point D.png
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• Point C2.png
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Welcome, @trusshelp148 !

My old eyes can barely distinguish anything in that image that you have included.
Could you improve it?

Lnewqban said:
Welcome, @trusshelp148 !

My old eyes can barely distinguish anything in that image that you have included.
Could you improve it?
Thank you! And of course, sorry for the blurry view. I've attached some more photos that I hope are more viewable.

Thank you!
I would treat both pulleys as one.
The tension in the cable is the same everywhere.
Are those 2000 kg-mass or kg-force?
That weight is your tension, pushing D and E down and compressing link 6 from both ends.

https://www.ecourses.ou.edu/cgi-bin/ebook.cgi?topic=st&chap_sec=03.2&page=case_sol

Links 4 and 5 must be in compression, transferring that load down to node C, link 1 and pivot A.
Link 1 must be in compression, while ling 2 is pulling hard from pivot B.
Link 3 is not doing much, at least in theory.

Lnewqban said:
Thank you!
I would treat both pulleys as one.
The tension in the cable is the same everywhere.
Are those 2000 kg-mass or kg-force?
That weight is your tension, pushing D and E down and compressing link 6 from both ends.

https://www.ecourses.ou.edu/cgi-bin/ebook.cgi?topic=st&chap_sec=03.2&page=case_sol

Links 4 and 5 must be in compression, transferring that load down to node C, link 1 and pivot A.
Link 1 must be in compression, while ling 2 is pulling hard from pivot B.
Link 3 is not doing much, at least in theory.
It is 2000 kg-mass, yes. How would I go about treating the pulley as one? Since it's the same cable going through D and E, do I not need to apply it to the links multiple times?

trusshelp148 said:
It is 2000 kg-mass, yes. How would I go about treating the pulley as one? Since it's the same cable going through D and E, do I not need to apply it to the links multiple times?
Doing a FBD for each pulley, you will see that two compression forces go down the two links that meet at each.
Treat the cable as in equilibrium (Tin = Tout)

Lnewqban said:
Doing a FBD for each pulley, you will see that two compression forces go down the two links that meet at each.
Treat the cable as in equilibrium (Tin = Tout)
Thank you! I understand now.

Lnewqban
Triangle CDE is loading node C with (19.6 x 2) kN (straight down).
Calculating moments about pivots A, and then B, you can determine how much vertical and horizontal forces each is loaded with.
Only then, you will be able to visualize how each link is working.

## 1. How do you determine the force on a truss with a pulley?

To determine the force on a truss with a pulley, you will need to use the principles of statics, specifically the equations of equilibrium. This involves analyzing the forces acting on each member of the truss and using the equations of equilibrium to solve for the unknown forces.

## 2. What is the role of a pulley in determining force and direction on a truss?

A pulley is a simple machine that changes the direction of a force. In the case of a truss, a pulley can be used to redirect the force on a member in a different direction, making it easier to analyze and determine the forces acting on that member.

## 3. How does the angle of the pulley affect the force on a truss?

The angle of the pulley affects the force on a truss because it changes the direction of the force acting on the member. This change in direction can result in a different magnitude of force being applied to the member, which must be taken into account when determining the overall forces on the truss.

## 4. What other factors should be considered when determining force and direction on a truss with a pulley?

In addition to the angle of the pulley, other factors that should be considered when determining force and direction on a truss with a pulley include the weight of the load being lifted, the tension in the rope or cable, and any external forces acting on the truss, such as wind or friction.

## 5. Are there any limitations or assumptions when using equations of equilibrium to determine forces on a truss with a pulley?

Yes, there are some limitations and assumptions when using equations of equilibrium to determine forces on a truss with a pulley. These equations assume that the truss is in static equilibrium, meaning that all forces are balanced and there is no movement. They also assume that the truss is rigid and that all members are connected by ideal pins or hinges. If these assumptions are not met, the equations may not accurately represent the forces on the truss.