Hydrostatics

For the raft to just sink, the total weight of the raft and the additional weight must be equal to the buoyant force acting on it. The buoyant force is equal to the weight of the water displaced by the raft. - The volume of the raft is given by: where is the mass of the raft, and is the density of the raft. The volume of the raft is: The buoyant force is the weight of the water displaced: Thus, the additional weight required to make the raft just sink is 80 kg, so the correct answer is (D).