# First moment and transversal shear

## Homework Statement

[PLAIN]http://img823.imageshack.us/img823/6601/unledpicturex.png [Broken]

## Homework Equations

$q = \tau/b$
$\tau = (VQ)/(Ib)$

I would like to calculate the shear flux in one row of nail. By taking the first moment for the upper board, calculating q and dividing by 2 I get the correct value.

My question is the following, why can't I take for example the left board? I would get Q=0, but what is the physical meaning of this? Why can't I use the left or right board to calculate the flux in the nails?

Thank you.

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