Example $2\mathrm{.}4$: The gate in Fig is $1\mathrm{.}5$ m wide, is hinged at point $B,$ and rests against a smooth wall at point $A.$ Compute $($a$)$ the force on the gate due to seawater pressure, $($b$)$ the horizontal force $P$ exerted by the wall at point $A,$ and $($c$)$ the reactions at the hinge $B.$