en carrying the cargo containers than when it is empty.","difficulty":7,"difficultyBand":"medium","totalMarks":6,"sourceTitle":null,"calculatorUse":null,"parts":[{"id":"ad92b411-e7ff-42db-8224-f1ba5c9a0b59","label":null,"content":"Explain why the barge floats when empty, and why it floats lower in the water when it is carrying the heavy cargo.","markscheme":"- Identifies that for an object to float, the downward force of its weight must be balanced by an upward upthrust force (equilibrium of forces) B1\n- States that upthrust is equal to the weight of the water displaced by the submerged volume of the barge (Archimedes' principle) B1\n- Explains that the empty barge has a relatively small weight, which is balanced by the upthrust from a small volume of displaced water B1\n- Explains that adding shipping containers increases the overall weight of the barge system B1\n- Explains that to remain floating, the upward upthrust must increase to balance this new, larger total weight M1\n- Connects this directly to sitting lower: the barge must submerge further to displace a larger volume of water to generate the required larger upthrust A1","marks":6,"order":0,"markingRubric":null,"explanation":{"methods":[{"id":"forces_and_displacement","label":"Balance forces and displacement","steps":[{"type":"text","order":0,"title":"Balance the empty barge","content":"For the empty barge to float without moving up or down, the forces must be in **equilibrium** (balanced): its downward weight equals the upward **upthrust** from the water. This earns **B1**.","highlights":[{"text":"The barge floats lower in the water when carrying the cargo containers than when it is empty.","location":"specification"}]},{"type":"text","order":1,"title":"Link upthrust to water","content":"Upthrust is equal to the **weight of the water displaced** by the submerged volume of the barge. *Displaced water* is the water that the submerged part of the barge takes the place of. This earns a further **B1**.","highlights":[{"text":"The barge floats lower in the water when carrying the cargo containers than when it is empty.","location":"specification"}]},{"type":"text","order":2,"title":"Explain the empty barge","content":"When empty, the barge has a relatively small weight. A small volume of submerged barge displaces a small weight of water, producing enough upthrust to balance that small weight. This earns the third **B1**.","highlights":[{"text":"first when empty","location":"specification"}]},{"type":"text","order":3,"title":"Add the cargo weight","content":"Putting heavy shipping containers on the barge increases the overall weight of the barge-and-cargo system. This earns **B1**.","highlights":[{"text":"loaded with heavy shipping containers","location":"specification"}]},{"type":"text","order":4,"title":"Increase the upthrust","content":"The loaded barge still floats, so its forces must again be balanced. Its larger downward weight therefore needs a larger upward upthrust. This earns **M1**.","highlights":[{"text":"The barge floats lower in the water when carrying the cargo containers","location":"specification"}]},{"type":"text","order":5,"title":"Explain the lower position","content":"To produce the larger upthrust, the barge must submerge further and displace a larger volume, so a larger weight, of water. Therefore it floats lower in the water. This earns **A1**.","highlights":[{"text":"floats lower in the water","location":"specification"}]}]}],"generatedAt":"2026-07-22T09:41:59.968Z","modelVersion":"gpt-5.6-terra+diagrams-1","explanationVersion":"v3"},"options":[]}],"options":[],"explanation":null,"firstAttemptFullMarks":null},{"id":"9883bc2d-46f2-468f-a52a-040a6f512d5c","revisionId":"84592123-0e90-43ba-97de-526d838146d0","questionNumber":null,"questionType":"LA","specification":"Figure 1 shows how the gauge pressure in a deep, non-homogeneous liquid ocean on a distant moon varies with depth below the surface.\n\n![Figure 1: A line graph showing gauge pressure in megapa

Pressure in fluids and upthrust

Question 16

Pressure in fluids and upthrust Questions

Pressure in fluids and upthrust

Question 16

Pressure in fluids and upthrust Questions