A scale reads 126 N when a piece of copper is hanging from it. What does it read (in N) when it is lowered so that the copper is submerged in water?

Answer 1

Draw a free body diagram - it should have 3 forces on it, weight, the buoyancy force (F_B), and the normal force (F_N). The sum of the forces equals zero so W = F_B + F_N

Calculate F_B by 1) calculate the mass of the copper using W = mg, 2) Calculate the volume the copper takes up using V = m/ρ where ρ is the density of copper (you can look this up), 3) the volume of the copper equals the volume of the displaced water and the buoyancy force equals the weight of that water. V_copper = V_water and m_water = V_water•ρ_water (look up the density of water). F_B = m_water•g (where g = 9.81)