$$ig$.3$

$$ig$.4$

$$ig$.$J

A long solid cylinder of radius $0\mathrm{.}8m$ hinged at point $A$ is used as an automatic gate, as shown in Fig. $4.$ When the water level reaches $5m,$ the gate opens by turning about the hinge at point A$.$ Determine $($a$)$ the hydrostatic force acting on the cylinder and its line of action when the gate opens and $($b$)$ the weight of the cylinder per $m$ length of the cylinder.