A rectangular gate $AB$ with $5m$ wide is hinged at $A$ as shown in Example $1$ The

weight of the gate, $W$ is $10kN.$ A horizontal strut force $P$ of $60kN$ is applied at

the top of the gate in order to hold the gate at its position. Determine the

maximum depth of water, $h$ that the gate can be retained.

Example $1$