A flak consisting of cope and drag has the following dimensions: length 300mm, width 200mm and total depth 200mm (cope height 50mm). A 150mm x 50mm cast iron block is to be cast. If the specific weight of cast iron is 78 kN/m3 and that of the mold sand 16 kN/m3, find lifting force on the cope created by buoyant force, weight of sand in the cope, the net force at the liquid-sand interface and additional weight to be kept on the cope.