# Force in Equilibrium

1. Jan 20, 2015

### CH Lee

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

2. Relevant equations

3. The attempt at a solution
I'm not sure about which topic it is asked. I think it's something about the centre of mass . Because the statement " The pole and the box do not change form" . The answer is
(1 + tan Θ)/(1 - tan Θ)

2. Jan 20, 2015

### BvU

What are (all!) the relevant equations for static equilibrium ?

Who do you think will have to carry more in the right picture ? B or A ? Why ?

The "don't change form" remark is to reassure you the center of gravity stays in the same place in the box/pole combo.

3. Jan 21, 2015

### CH Lee

A will carry more, I think it's because he's in higher position.
And is there any special formula for static equilibrium ? I just draw a triangle and use the formula F=ma.

4. Jan 21, 2015

### BvU

Hehe, you never had to carry something heavy down the stairs, I suppose ?

The conditions for equilibrium I hinted at in post #1 are in the first place $\Sigma \vec F = 0$ So that with your formula a = 0 $\Rightarrow$ v = constant. v = 0 remains v = 0. No translation.

But that's not enough. You also want no rotation, in other words: $\Sigma \vec \tau = 0$.
And now the positions where the forces act come in the expressions.

Last edited: Jan 21, 2015
5. Jan 21, 2015

### siddharth23

F = ma comes into question when acceleration comes into question. Here, a = 0 and v = 0. All forces balance each other out. FA and FB act vertically upward. In which direction do you think 'W' acts?

6. Jan 21, 2015

### DEvens

The forces are vertical. That is a constraint on the answer given by the question statement. In an actual case of carrying a couch down a ramp the people doing the carrying probably would not arrange their hand-holds that way, but the problem requires it.

The pole is not rotating while it is being carried.