# Statics problem

1. May 30, 2007

### Mark_iv

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

2. Relevant equations

i dont know :(

3. The attempt at a solution

I tried but the working is in a notepad, plus I wasnt getting anywhere anyway!

I know its a long questions but this example is essential to my study, any help is largely appreciated!

Thanks in advance!

2. May 30, 2007

### mjsd

I'll start by teaching you how to do part (i) the center of mass.

1. choose an origin (in this case the best point to choose would be the pivot point)
2. work out the location of the center of mass of the bar and the crate. Both is easy since bar has uniform mass distribution ie. mid-point is the location; and crate can be treated as point mass anyway
3. know your formula:
in x-component of centre of mass
$$(m_1+m_2)x_{cm}=m_1 x_1 + m_2 x_2$$
for y:
$$(m_1+m_2)y_{cm}=m_1 y_1 + m_2 y_2$$

Masses are given, $$(x_1,y_1)$$ and $$(x_2,y_2)$$ are the location of the center of mass of the indivdual $$m_1$$ and $$m_2$$ which you will have to work out using some geometry (ie. sin, cos)

apart from that you get (as you stated) $$x_{cm}\approx 1.28m, y_{cm}\approx 0.67m$$ from the pivot point. try it!

sure it is essential to your study...looks very much like a typical 1st year undergrad exam question

Last edited: May 30, 2007
3. May 30, 2007

### PhanthomJay

Your other questions can be solved with a bit of trig and by using Newton's first law: sum of forces in x direction =0; sum of forces in y direction =0; sum of torques about any point =0. You must show some attempt at your work before we can help further. HINT: Since the wall is frictionless, there can be no vertical force reaction at the wall.

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