Hi, I have an issue with a question I am trying to answer and I don't seem to be getting the correct answer... Question A 950kg cylindrical can buoy floats vertically in sea water, the diameter of the buoy is 0.860m. Calculate the additional distance the buoy will sink when a 70kg man stands on top of it. Attempt OK, so I know that for a floating object, the buoyant force is equal to the weight of the object, so calculating for just the cylinder on its own... Density of sea water (ρ) = 1030kg⋅m-3 Surface area of cylinder (A) = πr2=π(0.860/2)2=0.581m2 Weight of cylinder (Wc) = 950kg⋅9.8ms-2=9310N Fb=ρVg=ρAhg=Wc=9310N 9310N=1030kg⋅m-3⋅9.8m⋅s-2⋅0.581m2⋅h 9310N=5865kg⋅ms-3⋅h rearranging for h h=9310N/5865kg.ms-3 h=1.59m So that should mean that 1.59m of the cylinder is submerged in water when it is just the cylinder. Then I can do exactly the same again, with the additional 70kg on top of the cylinder... Weight of cylinder and man (Wcm) = (70kg + 950kg)⋅9.8ms-2=9996N Fb=ρVg=ρAhg=Wcm=9996N 9996N=1030kg⋅m-3⋅9.8m⋅s-2⋅0.581m2⋅h 9996N=5865kg⋅ms-3⋅h rearranging for h h=9996N/5865kg.ms-3 h=1.70m So now I can just calculate Δh = 1.70m - 1.59m = 0.117m (calculated using non rounded figures) I know I could have saved a lot of working out and just done the the calculations for 70kg only, neglecting the cylinder and got the same answer. According to my text book, the answer to this question is 0.177m Have I done something stupid here (which is entirely plausible)?