Moments using force and distance.

[weedannycool]

Homework Statement

The 4-kN force F is applied at point A. Compute the
moment of F about point 0, expressing it both as a
scalar and as a vector quantity. Determine the coordinates
of the points on the x- and y-axes about which
the moment of F is zero

Homework Equations

m=fd

The Attempt at a Solution

i think that i need to find the distance from F to the origin that is perpendicular. since the moment is always perpendicular to the line of action.

 

[PhanthomJay]

Yes, I think the easiest way is to break F into its x and y components, then solve for the moment about O by algebraically summing the moments produced by these component forces. Moments can be computed this way (force times perpendicular distance), but that is not the only way. Watch plus/minus signs!

 

[weedannycool]

is there a simpler way to do this. i can't get my head round it. thanks

 

[PhanthomJay]

is there a simpler way to do this. i can't get my head round it. thanks

You can use M=rFsintheta, where r is the magnitude of the position vector between O and A, F stars as itself, and theta is the included angle in between F and the position vector. I find it easier to break F into its x and y components, and then M_o = F_x(y) + F_y(x)