The reasoning behind why a person falls fast like a cannonball is because the weight of a person is concentrated heavily at one point on his body depending on the side which faces vertically and perpendicularly to the ground hence much of the air resistance is thwarted. Notice that if a person is falling horizontally, the person will fall slowly. Falling horizontally with more area will result to more air resistance because the weight will be evenly distributed around it. That is the reason why parachutes and other objects with wider area and evenly distributed weight fall slower than a human without parachute.
