# Homework Help: Unsure of mechanics problem, circular door on hinge..

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1. Sep 17, 2015

### aaroon

1. In the attached imjage, the centre of gravity of an open door acts at G equal to 255N;
a) Determine the x,y,z, components of reaction at the hinge A in equilibrium
b) Determine the force along CB

Little stuck with this problem, obviously this falls under resolving forces. I assumed Az,Ay = 0 as gravity is acting straight down and Az= 255N - (verical component of reaction given by CB). Any help would be appreciated :)

[PLAIN]http://www.imgur.com/V9G2Kz7[/CENTER] [Broken]​

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Last edited by a moderator: May 7, 2017
2. Sep 17, 2015

### BvU

Hello Aaroon, welcome to PF !

As much as I'd like to help you, I can't make heads or tails out of this post (well, see below...). Would you be so good as to sort out things using the template that accidentally got deleted (it is compulsory in PF, we in fact aren't allowed to assist if it's missing...) ?

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

2. Relevant equations

3. The attempt at a solution

It seems they want the components of the force on A and along CB.

The lot is in equilibrium, so you should be able to set up a force balance plus a torque balance. The Ax , Ay and Az you provide don't give a balance in either of these two...

3. Sep 17, 2015

### Baluncore

Is the line CB a strut that supports the door in the open position, ie door horizontal ?
Does the strut CB bear on a point on the circumference of the door, an angle theta from the y axis ?

4. Sep 18, 2015

### aaroon

Hi Baluncore, thanks for your reply, my understanding is CB supports the door in the open position as you say.

That is also my question, I would assume so otherwise the angle has no purpose.

5. Sep 18, 2015

### haruspex

Meaning the components of the reaction at the hinge? No, all three will be nonzero.
Are you expected to work in terms of resolved components or vectors (including vector products)? I suggest the second would be neater.

6. Sep 18, 2015

### aaroon

I believe resolved components but haven't been told explicitly.

7. Sep 18, 2015

### haruspex

Have you worked with vector products?

8. Sep 18, 2015

### Baluncore

The lack of a radius symbol suggests the strut contacts the circumference at the radius of 0.9m in direction theta.
I think the question has now been resolved, so I'll leave you to find the answers.