Why is my torque calculation incorrect for this simple force problem?

[VinnyCee]

http://img403.imageshack.us/img403/879/problem4998tl.jpg

Here I resolved the forces:

$$\overrightarrow{F_{A_x}} = \left(375sin30\right)N$$

$$\overrightarrow{F_{A_y}} = \left(375cos30\right)N$$

Here is the r vector (I think):

$$\overrightarrow{r_{AP}} = \left(4\hat{i} - 3\hat{j}\right)m$$

But when I do r X F, I get something wrong, what do I have to do to solve this simple problem?

 

[vaishakh]

Let the Centre of AP be M, then MP is the radius Vector I guess from what I understood after seeing the picture. You know the co-ordinate of A and P, so you can find the co-ordinates of M.

 

[nrqed]

http://img403.imageshack.us/img403/879/problem4998tl.jpg

Here I resolved the forces:

$$\overrightarrow{F_{A_x}} = \left(375sin30\right)N$$

$$\overrightarrow{F_{A_y}} = \left(375cos30\right)N$$

Here is the r vector (I think):

$$\overrightarrow{r_{AP}} = \left(4\hat{i} - 3\hat{j}\right)m$$

But when I do r X F, I get something wrong, what do I have to do to solve this simple problem?

The y component fo your force should be negative.
Also, in calculating the torque, the vector r should go from the axis of rotation toward the point where the force is applied.

Patrick