A circular opening $2\mathrm{.}5$ m diameter in a vertical side of tank is closed by a disc of $2\mathrm{.}5$ m diameter which can rotate about a horizontal diameter. Calculate $($i$)$ The forces on the disc. $($ii$)$ The Position of Centre of pressure $($iii$)$ The total torque required to maintain the disc in equilibrium in vertical position when the head of water above horizontal diameter is $3\mathrm{.}5$ m