# Homework Help: Are my answers correct? (3D statics)

1. Jul 1, 2011

### Femme_physics

I don't have the solution manual answer for this problem, can anyone help please confirm my answers are correct?

1. The problem statement, all variables and given/known data

http://img860.imageshack.us/img860/6118/40893341.jpg [Broken][/QUOTE]

On a smooth horizontal weightless surface ABDC acts at the center a vertical force of 600 [N]. The surface is connected to the wall through axes A and B and supported by shaft CE.

A) Calculate reaction at CE
B) Calculate reactions at axes A and B. Presume the forces at the B axis are at the X and Y direction only.

3. The attempt at a solution

This is my solution attempt

http://img204.imageshack.us/img204/2712/20112011a.jpg [Broken]

http://img834.imageshack.us/img834/6539/20112011b.jpg [Broken]]

And here below in the thumbnail I have attached my friend's attempt. He's smart, but new to 3D statics, and I don't understand how what he did makes sense. In fact it contradicts my results and methods.

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• ###### sp2.jpg
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Last edited by a moderator: May 5, 2017
2. Jul 1, 2011

### I like Serena

I don't understand what your friend did.
It looks rather complex, but his answers are wrong.

Reducing the problem to 2D makes it much easier to follow what you did.

However, you also made a mistake.
It starts with your zx-view, when you calculated TCEzx where you used TCEy, but you should have used TCEx.
Same for the calculation of TCEz.

As a consequence, your Bx, Ax, and Az are wrong too.

Last edited by a moderator: May 5, 2017
3. Jul 1, 2011

### Femme_physics

I'll tell you why, I'm used to "y" being up so I keep confusing myself :tongue:

Thanks a bunch will correct it today

4. Jul 2, 2011

### I like Serena

But "y" is up!!! :tongue2:

5. Jul 2, 2011

### Femme_physics

It's "up" in the 3D drawing. But in the 2D ones, it's always psychologically my "up"-- something which I still haven't completely gotten rid off.

6. Jul 2, 2011

### I like Serena

Uhh, it's up in 3D and it's up in your yx-view and it's up in your yz-view. :uhh:

It's just that in 3D normally z is always up, and in the yz-view z should be up too!

7. Jul 2, 2011

### Femme_physics

Yes, I said psychologically "up" as in the sense that's it's pointing towards the upper part of the page that I'm writing on heh, I still haven't gotten over it is what am saying

8. Jul 2, 2011

### I like Serena

Still, in this problem y is pointing up to the physical top of your page.

I think you've gotten over that just fine!
You're already used to the fact that z should be pointing up to the physical top of your page.

The challenge in this problem is to apply the direction of the y-coordinate mathematically, carefully without making assumptions based on the 3D you're already used to.
That really makes this problem harder than it has to be.

9. Jul 2, 2011

### Femme_physics

not if you're looking at the xz view

10. Jul 2, 2011

### I like Serena

Oooooooooooooooooooooooh!
(Thanks for clarifying that! )

11. Jul 2, 2011

### Femme_physics

Last edited by a moderator: May 5, 2017
12. Jul 2, 2011

### I like Serena

Yay!

You didn't ask for it, but I give it the ILSe-stamp-of-approval.
Btw, whatever happened to that item that I didn't put a stamp-of-approval on?

13. Jul 2, 2011

### Femme_physics

Maybe I didn't ask, but I secretly desired!
Thanks :mrgreen:

"Btw, whatever happened to that item that I didn't put a stamp-of-approval on?
"

To be amended, rest be assured!