Weight A weighs 50 pounds. weight B weighs 100 pounds. if A is placed 6 feet from the pivot, how far must B be placed from the pivot in order for the bar to achieve balance?

To achieve balance, the momentum on both sides must be equal so that it cancels out. Momentum is simply the product of mass and distance, therefore:

50 pounds * 6 ft = 100 pounds * X

X = 3 ft

Hence B must be placed 3 ft from the pivot.