Statics problem

[Mark_iv]

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

http://img76.imageshack.us/img76/7307/staticsir4.jpg

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!

[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!

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

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

[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.