# 3D statics - looks impossible to solve

• Femme_physics
In summary, the conversation discusses a difficult 3D mechanics problem involving a weightless beam connected to a wall and supported by two cables. The conversation also mentions the difficulty of solving the problem and the use of multiple equations to find the unknowns. The conversation ends with the acknowledgement that the problem can be solved but may require a system of equations.
Femme_physics
Gold Member
This question was on my mechanics test but I skipped it. It seemed kinda crazy.

## Homework Statement

In the drawing is described a weightless beam AC connected to the wall through joint C. The beam is supported by two cables, BE and AD, connected to the wall. At the end of the beam at point A, acts a vertical force of 880 [N]

A) Calculate the tension in cables AD and BE

B) Calculate reaction at joint C

http://img685.imageshack.us/img685/3816/birdplane.jpg

## The Attempt at a Solution

I'll spare you the rest of the equations, since no matter what view I'm looking at ...too many unknowns at sigma torque equation!

http://img16.imageshack.us/img16/5538/try3d1.jpg

http://img23.imageshack.us/img23/244/try3d2.jpg

Last edited by a moderator:
What happened to the sum of forces equations?

That would just end up adding another unknown, Ay! So I'd end up with 3 unknowns. At least here I got 2 unknowns!

Can you admit at least this is the most difficult 3D problem we've encountered yet?

Also, how'd you get 200+ posts more than me?!?? I've been slacking!

Still, writing up all equations will get you your answer.
Whereas getting stuck at more unknowns than equations, will not get you your answer. ;)

How many equations do you think you can get?
And which unknowns do you think you would have?

Femme_physics said:
Can you admit at least this is the most difficult 3D problem we've encountered yet?

Hmm, I don't think so.

Femme_physics said:
Also, how'd you get 200+ posts more than me?!?? I've been slacking!

Well, I've been posting more in GD than you have...

You should have 6 equations...

I like Serena said:
You should have 6 equations...

6 equations! and you're telling me this is NOT the hardest problem we've done??

In ALL other 3D statics problems, we were able to take just one view, do one moment equations, and find one unknown, and then from that point on it was a smooth ride. There were NEVER systems of equations!

I hope I don't appear lazy! I just want to gauge the craziness of this question before carrying on to actually solve it

Well, you had a number of other problems where you needed 3 views.
And often you did not write out all the equations, although you did use them.
It's just that you already saw beforehand which way to go and getting a smooth ride.

In statics I believe you did not have to solve systems of equations yet, as opposed to electronics.
Perhaps in this one you do have to solve a system of equations.
But you're good at that now, after all the exercises in electronics!

Actually I solved many statics problems with 3 equations 3 unknowns! I just didn't post them here because they were easy

But none of them were 3D!

Well, you had a number of other problems where you needed 3 views.
And often you did not write out all the equations, although you did use them.
It's just that you already saw beforehand which way to go and getting a smooth ride.

In all other problems, 1 equation was enough to start with. In here, you start with 6! Definitely harder, but still, seemingly solvable. I just wanted to see the direction, I'll have to do the final blow another time...^^ Thanks

## 1. How does 3D statics differ from 2D statics?

3D statics involves analyzing forces and moments in three-dimensional space, while 2D statics only considers forces and moments in two-dimensional space.

## 2. Is 3D statics more difficult to solve than 2D statics?

Yes, 3D statics is typically more difficult to solve because it involves more variables and equations compared to 2D statics. However, with the use of computer software and advanced mathematical techniques, it is possible to solve complex 3D statics problems.

## 3. Can 3D statics be applied to real-world situations?

Yes, 3D statics is commonly used in engineering and physics to analyze the structural stability of buildings, bridges, and other structures in three-dimensional space. It is also used in the design and analysis of machines and mechanical systems.

## 4. What are some common challenges when solving 3D statics problems?

Some common challenges include identifying and understanding all the forces and moments acting on a system, choosing an appropriate coordinate system, and setting up and solving the necessary equations.

## 5. How does 3D statics relate to other areas of science and mathematics?

3D statics is closely related to other areas of science and mathematics, such as vector calculus, linear algebra, and mechanics. It also has applications in fields such as robotics, aerospace engineering, and biomechanics.

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