# Question on Shear Flow

1. Mar 17, 2008

### suspenc3

1. The problem statement, all variables and given/known data
The beam is fabricated from four boards nailed together as shown. Determine the shear force each nail along the sides C and the top D must resist if the nails are uniformly spaced at s=3in. The beam is subjected to a shear of V=4.5 kip.

I understand how to the problem...i thought anyways. The only part I dont understand is the calculation of Q for the top D. In my head, I would calculate it as: $$Q= y'A'$$ where y'= centroid of top board-centroid of the fabrication. The area would be the area of the top board. In the solution they use the area of the vertical board in the calculation. How do you know what board area to use in these types of questions?