Question

I am re-posting this question in hopes that another person will answer what I am really looking for.

Please (pretty please) don't post a two page write up of how to do this problem, there are already multiple answers to this problem, it is not what I need help with.

A trough is filled with a liquid density of 840 kg/m3 The ends are equalateral triangles with a side length of 8m and the vertex at the bottom.

Find the hydrostatic force on one end of the trough. (again, please dont answer this part)

My question:

I am wondering why the length of our sample strip is 8 - 2xi /Sqrt(3) ? Isnt the length of the sample strip just 2xi/Sqrt(3)? Why does the length depend on 8 (the triangles side length)? This seems to be a pretty key concept...

Thank you