In a uniform gravitational field, the center of gravity of an object is at the same point as the center of mass of the object, and the work done to lift an object is the weight of the object multiplied by the distance that the center of gravity of the object is raised: work = (total weight of object) (distance the center of gravity of the object is raised). In the high jump, this explains the effectiveness of the "Fosbury Flop", a technique in which the jumper assumes an inverted U position while going over the bar (Fig. 30). In this way, the jumper's body goes over the bar while the jumper's center of gravity goes under it, so a given amount of upward thrust produces a higher bar cleared. If the center of gravity of an object is known, some work problems become easy. bar cm Fig. 30 32. A cylinder is filled to a depth of 2 feet with 40 pounds of liquid. How much work is done pumping the liquid to a point 7 feet high? (How high is the center of gravity of the liquid, and how much must it be raised?)