Question regarding Moments of forces

[ZARman]

Hi
I have a question regarding Moments of forces
When in equilibrium we have a lever hinged at B which is in between A which is 120' to B and C which is Flat .. A force is applied to A at 50'(P) and another force to C at 70'=100N
So breaking down P into components you get P Sin 50 (perp to A) this is when working working out moments .. but then the lecturer used P Cos 10(parallel to ground) when doing the resultant forces . so now my question is when do i use which angles?

 

[Doc Al]

so now my question is when do i use which angles?

When finding moments, you want the component perpendicular to the moment arm. Thus P sin50, since the force is 50 degrees to the line A-B.

When finding components for resultant forces, use the horizontal and vertical axes. The force P is 10 degrees to the horizontal, so P cos10 will give the horizontal component.

 

[ZARman]

Thanks ill work by the rule .