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.