Determine the smallest dimension $d$ that will prevent the dam from overturning about its end $A.$

The concrete "gravity" dam is held in place by its own weight

$($Figure $1).$ The density of concrete is ${}_c=2\mathrm{.}5M\frac{g}{m^3},$ and water has

a density of ${}_w=1\mathrm{.}0M\frac{g}{m^3}.$ Suppose that $a=1\mathrm{.}5m,h=7\mathrm{.}5m.$

Figure