Statics Help: Support Reactions

1. Apr 12, 2007

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http://img177.imageshack.us/img177/2355/staticsqn5.th.jpg [Broken]
I understand the problem here, what I don't see is how to find the support reactions. Since at each joint we have more than two unknowns I have to find the support reactions. I have the answer to the problem. Could someone tell me how to find the support reactions? It seems like I need to take the moments about G and or F to get the support reactions at the pin at A and the rocker at E. Is this true?

Last edited by a moderator: May 2, 2017
2. Apr 12, 2007

robphy

It seems that you have three unknown [rectangular] components, two at A and one at E.

For the structure as a whole, did you write down Newton's laws (for statics) $$\vec F_{net}=\vec 0$$ and $$\vec \tau_{net}=\vec 0$$, which yields three scalar equations [for this planar problem].. and hence three linear equations in three unknowns? By choosing to evaluate moments about A, you can simplify your system.

3. Apr 12, 2007

Right that is what I assumed! However, I'm kind of working backwards throught this text. So I'm not finding the correct moment equations.

4. Apr 12, 2007

robphy

What are your explicit equations? (in terms of P1, P2, a, e)

5. Apr 12, 2007

At pin A we have $$A_x and A_y$$ at the rocker E we have $$E_y$$.

So shouldn't the moments be:

$$M_A = 20kn-1.5A_y$$

I'm confused now! I know this is so easy when i finally see it

6. Apr 12, 2007

robphy

Shouldn't it be "sum of the moments about A"
$$M_A= (-1)(a)P_1+(-1)(3a)P_2+(1)(4a)E_y$$ ?

7. Apr 12, 2007