Finding Tension in Cables: How to Use Moments to Solve for Unknowns

In summary, the conversation involves discussing a problem involving finding the tension in cables supporting a sign. The initial attempt at a solution involves using moments and considering the force of the sign hanging from one of the cables. A suggestion is given to draw a free body diagram and find the sum of forces in the y direction, but the person is still unsure of how to proceed. Another suggestion is to break the figure into separate bodies and write equations for each one. A final suggestion is to treat the entire figure as one object and use two equations to analyze the tension in the cables. It is then discovered that the problem statement is incorrect due to the dimensions shown.
  • #1
Nanart
13
0

Homework Statement



pysicssign.jpg




Obviously the picture is not to scale

The Attempt at a Solution


I really have no ides where to start I assume you have to use moments to find the tension in each cable but I am really not sure how to go at it.
I think the 20 N force hanging from the sign would only act through the one cable and wouldn't effect the other cable because it is the same distance from the end as the support cable.

Thanks for the help
 
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  • #2
Start off by drawing your free body diagram. Since the material has a constant density its CG will act at the center of the sign. Next, you find the sum of the forces in the y direction. Also you are correct in saying that you can sum the moments. Just one pointer, try finding the point with most forces acting at it.
 
  • #3
djeitnstine said:
Start off by drawing your free body diagram. Since the material has a constant density its CG will act at the center of the sign. Next, you find the sum of the forces in the y direction. Also you are correct in saying that you can sum the moments. Just one pointer, try finding the point with most forces acting at it.

I really still don't know where to start can someone go over the steps in doing this question
Thanks
 
  • #4
Break the figure apart and treat each body as a separate FBD. Show the forces acting on that body and then start writing your equations.
 
  • #5
Dr.D said:
Break the figure apart and treat each body as a separate FBD. Show the forces acting on that body and then start writing your equations.

Hmm that is too much work, he can do this using 2 equations by treating the whole thing as one object and analyze the tension in the cables alone.
It seems he wants us to do it for him but if he could just separate the body from the wall, then sum the forces in the y direction, and sum the moments (or torques) about either the point where Ta or Tb is acting then he is done.
 
Last edited:
  • #6
A little bit of discovery is a wonderful learning experience.
 
  • #7
Haha, i'll place it as a spoiler then ;)
 
  • #8
The problem statement is incorrect, based on the dimensions shown. One of the rods will not be in tension.
 

Related to Finding Tension in Cables: How to Use Moments to Solve for Unknowns

1. What is tension and why is it important to find on cables?

Tension refers to the force applied to a cable that creates a pulling or stretching effect. It is important to find tension on cables because it helps determine the strength and stability of the cable, and can ensure that it is able to support any loads placed on it.

2. How do you calculate tension on cables?

Tension can be calculated by using the formula T = F x L, where T is the tension, F is the force applied, and L is the length of the cable. It is important to note that the force applied must be in the same direction as the cable.

3. What factors affect tension on cables?

There are several factors that can affect tension on cables, including the weight of the load placed on the cable, the angle at which the cable is pulled, and the properties of the cable such as its length, diameter, and material.

4. How do you measure tension on cables?

Tension on cables can be measured using a tension meter or dynamometer, which are devices specifically designed for this purpose. Alternatively, it can also be measured indirectly by using strain gauges or load cells.

5. Can tension on cables be too high or too low?

Yes, tension on cables can be too high or too low. If the tension is too high, it can cause the cable to become overstretched and potentially snap, while too low tension can result in the cable sagging and not being able to support the intended load. It is important to find the appropriate tension for each cable to ensure safety and functionality.

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