A gate in the vertical face of a dam has the shape of a semicircle of radius 4 ft whose top edge is its diameter (also parallel to the water surface). Find the total force of water (62.4 pounds per cubic foot) on this gate if its top is 10 ft beneath the surface of the water.

Ugh, I feel like I'm drowning!!! (Pardon the pun) Any help at all would be appreciated... I think I just have trouble "visualizing" what's going on, and getting started. Thanks in advance.