Deriving width formula for hydrostatic force on a triangular lamina

[sdaysley]

i have this example of a hydrostatic force on a plane surface.

what i don't understand is how the width of the integral strip is derived

it says w(s)=b(s-s1)/L i don't understand how this comes about?

would be really greatful if anyone could direct me i can't find anything on triangular lamina double integration :S

cheers!

 

[andrien]

just draw a perpendicular from the vertex on the base and then use the property of similar triangles.
w/b=S-s1/L

 

[sdaysley]

great thanks for that