In Figure $11,$ A circular opening, $2\mathrm{.}5m$ diameter, in a vertical side of tank is closed by a disc of $2\mathrm{.}5m$ diameter which can rotate about a horizontal diameter. Determine: $[168\mathrm{.}6$ kN; $3\mathrm{.}61m$;$18\mathrm{.}55kNm]$

i$.$ the force on the disc

ii$.$ the torque required to maintain the disc in equilibrium in vertical position when the head of water above horizontal diameter is $3\mathrm{.}5m.$