Statics Help: How to Find Support Reactions for Structural Problems

[RadiationX]

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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?

 

[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.

 

[RadiationX]

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

 

[robphy]

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

 

[RadiationX]

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

 

[robphy]

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

 

[RadiationX]

Yes that is correct. I see now my mistake(s)