Coplanar equilibrium (mechanics)

[kring_c14]

could you pls give me an idea what to do in # 4.13...?? I'llbe the one to solve, what will I use?

http://www.imagevimage.com/images/CCI11042007_00000.jpg

 

[radou]

Since you have a free body diagram in the picture, you should have an idea of where to start.

 

[kring_c14]

uhmmm, that's the problem..im really not that familiar with moments and stuff.. could you give me a hint? plsssss...

 

[radou]

uhmmm, that's the problem..im really not that familiar with moments and stuff.. could you give me a hint? plsssss...

OK, which forces are acting on the roller?

 

[kring_c14]

well what I did was this one$$\sum Fx= Pcos20-Nsin20-Fsin70=0$$
$$\sum Fy=P sin20+Ncos20-Fcos70-120=0$$

then, i don't know what to do...

 

[radou]

well what I did was this one$$\sum Fx= Pcos20-Nsin20-Fsin70=0$$
$$\sum Fy=P sin20+Ncos20-Fcos70-120=0$$

then, i don't know what to do...

If the x-axis is along the incline (which is visible from the FBD), the your equations are not correct.

 

[kring_c14]

so how do I make it right?

 

[radou]

so how do I make it right?

Well, since we're talking about equilibrium, sum up the forces in the x and y directions, and set them equal to zero.