Statics/Equilibrium Physics question-- Two weights and a single pulley

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Homework Help Overview

The problem involves a system in equilibrium with a 60 lb collar "A" on a vertical rod connected to a 65 lb counterweight "C" via a pulley. The objective is to determine the height "h" between points "A" and "B" and the horizontal force "N" acting on collar "A". The setup includes a continuous rope from "A" to "C" and a specified horizontal distance of 15 inches between "A" and "B".

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the forces acting on collar "A" and the relationship between the tension in the rope and the angles involved. There is an exploration of how to express the tension in terms of the height "h" and the horizontal distance. Some participants question how to set up the equilibrium equations correctly.

Discussion Status

Participants are actively engaging with the problem, offering suggestions on how to approach the equilibrium conditions. There is a focus on breaking down the forces and using trigonometric relationships to express the tensions involved. However, there is no explicit consensus on the next steps or a clear path forward.

Contextual Notes

Participants note the challenge of visualizing the problem and the complexity of relating the various forces and angles. There is an acknowledgment of the need for a clearer understanding of the relationships between the components involved in the equilibrium.

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Homework Statement


The 60 lb collar "A" is on a friction-less vertical rod and is connect to a 65 lb counterweight "C". Determine the value "h" (which is the height between "A" and "B") for which the system is in equilibrium. Also, find the horizontal force "N" acting on collar "A".
Here is a rough typed up picture of what the picture looks like, the zeros (0) are empty space

<--15in-->
00000000B0 ^
0000000/0|0 |
000000/00|0 |
00000/000|0 |
0000/000 C0 h
000/0000000 |
00/00000000 |
0/000000000 |
A0000000000v

The horizontal distance between A and B is 15 in. There is a pulley at B and a rope/string going from a A to B, and B to C. From what I can tell, the rope is continuous from points A to C. I have no idea where to get started on this or how to ultimately find h or the horizontal force acting on point A.
A is a 60 lb weight.
C is a 65 lb weight.

Homework Equations


All I have so far are these few things:
∑Fx = 0
∑Fy = 0
TBC = 65 lb
TBA = 65 lb

The Attempt at a Solution


I really don't know where to begin with this problem. I'm thoroughly confused as to how I should go about finding "h" or the horizontal force at "A", and I haven't been able to find similar problems to this one. If anyone can help me out, it'd be much appreciated.
 
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Hello Zubb, and welcome to PF.

Nice picture.. :smile:
As a first step it might be nice to consider only A and the section AB of the rope. What vertical force is needed to keep A from moving up (or down) ?
The rope can only exercise a force in a direction along the rope. With one component known and the tangent of the angle expressed in h and the 15 in, you have an expression for the total tension in the rope. Then it's time to bring B and C back in the considerations.
 
Ok...

So according to what you just said, I should have this at my disposal:
TBAy = 60 lb.
tanθ = h/15 in. --> θ=tan-1(h/15 in.)
If TBA = TBAy x sinθ
then TBA = TBAy x sin(tan-1(h/15 in.))
If TBA = TBAx x cosθ
then TBA = TBAx x cos(tan-1(h/15 in.))

Right?

And then when I bring TBC to put all this into the ∑Fx and ∑Fy equations, and I end up with this:
∑Fx = TBA/(cos(tan-1(h/15 in.))) = 0? [substituted TBAx out]
∑Fy = A[-60 lb.] + C[-65 lb.] + TBA/(sin(tan-1(h/15 in.))) + TBC[65 lb.] = 0 [substituted TBAy out]

I'm terribly sorry, but I'm not seeing how this helps me... :cry:
I really do appreciate this help though. :biggrin:
 
Well, you have TBA,y, you have TBA and you have a relationship with one unknown, h.
What can be easier ? :smile:
 

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