A $6$ m$-$high, $5$ m$-$wide rectangular plate blocks the end of a $5$ m$-$deep seawater channel $($salinity $35$ ppt$,$ Sg $=1\mathrm{.}028,=1\mathrm{.}15$x$10-6$ m$2/$s$).$ As shown in Figure $1,$ the plate is hinged about a horizontal axis along its upper edge, through point A$,$ and is restrained from opening by a fixed ridge on the channel floor, at point B$.$ Figure $1$ Seawater channel barrier gate$($a$)$ What is the mass density, specific weight, and absolute viscosity of this fluid?