Force in Equilibrium

  • Thread starter CH Lee
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  • #1
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Homework Statement



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Homework Equations




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)
 

Answers and Replies

  • #2
BvU
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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
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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.
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
BvU
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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:
  • #5
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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.
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
DEvens
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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.
 

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