Use the approximate pressure-density relation for a "soft" liquid, dp=adp, or p=p + a (p-p) where a is the speed of sound and (P., P.) are the conditions at the liquid surface z = 0. Use this approximation to derive a formula for the density distribution p(z) and pressure distribution p(z) in a column of soft liquid. Then find the force F on a vertical wall of width b, extending from z = 0 down to z = -h, and compare with the incompressible result F = poghb/2.