There is a square board with two nails in corner A and B. We apply a torque M to the square board. Nail A can move freely on a track only in the $x$ direction and B only in the $y$ direction. The question is to calculate the normal forces from the tracks to the nails. My problem is that I can't seem to find a way to calculate mathematically the accelerations in points A and B. The solution just gives them as stated below like it is something obvious, (but it isn't for me):
$\textbf{a}_A = l \alpha \textbf{e}_x$
$\textbf{a}_B = l \alpha \textbf{e}_y$
where $\alpha$ is the angular acceleration of the board.
How can I see that mathematically from a formula?
