# Homework Help: Equilibrium - Calculate forces

1. Oct 26, 2008

### Naldo6

Here is the picture of the Problem in the atachments ok... i need to calculate F1 and F2.

Any suggestions plz.... i don't know how to begin the exercise. ok help plz

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2. Oct 27, 2008

### tiny-tim

Hi Naldo6!

In problems like this, you can take components in a direction, or you can take moments about a point.

Try moments!

3. Oct 27, 2008

### Naldo6

Re: Equilibrium

how i try that?....

4. Oct 28, 2008

### tiny-tim

moments of forces

Moments are like a see-saw … the smaller you are, the further away you have to be to balance someone bigger.

In equilibrium, the moments all add up to zero (just like ordinary components of force).

The moment of a force about a point is the force times the distance from that point.

Just choose a point, and calculate all the moments.

5. Oct 28, 2008

### Naldo6

Re: Equilibrium

is this correct for F2:

0=-F3D1 - (D1+D2)F4 - (D1+D2+D3)F5 + (D1+D2+D3+D4)F2 - ((D1+D2+D3+D4)/2)(9.8)

then F2= [ F3D1 + (D1+D2)F4 + (D1+D2+D3)F5 + ((D1+D2+D3+D4)/2)(9.8) ] / (D1+D2+D3+D4)

right?...

and then F2 + F3 + F4 + (9.8)(mass) = F1 + F2 to calculate the other righ?...

i do that but i dont get my answers...

6. Oct 28, 2008

### tiny-tim

Hi Naldo6!

Did you mean to type

F2= [ F3D1 + (D1+D2)F4 + (D1+D2+D3)F5 + ((D1+D2+D3+D4)/2)(9.8)(mass) ] / (D1+D2+D3+D4)?

(which you could simplify to F2= (9.8)(mass)/2 + [ F3D1 + (D1+D2)F4 + (D1+D2+D3)F5] / (D1+D2+D3+D4))

If so, that should be right.

Do D1 etc have numbers?

If so, show us the full calculation, and maybe we can see the mistake.

7. Oct 28, 2008

### Naldo6

Re: Equilibrium

ty... i get the correct answer with my formular, i just wa smissing my mass in the F of gravity ... ty a lot