SCHOOL OF CIVIL AND ENVIRONMENTAL ENGINEERING
UNIVERSITY OF THE WITWATERSRAND
Fluid Mechanics and Hydraulics (CIVN3024A)
Tutorial: Buoyancy
1. What length of 100 mm by 300 mm timber (relative density = 0.5) will just support a 47.0 kg boy in
fresh water if he stands on the timber?
(Ans. 3.13 m)
2. An iceberg (ρ = 913 kg/m3 ) floats in salt water (ρ = 1025 kg/m3) with a volume of 595 m3
above the surface. Determine the total volume of the iceberg.
(Ans. 5445 m3)
3. A ship with vertical sides near the water line weighs 40,000 kN and draws 7.0 m in salt water (ρ =
1025 kg/m3) . The discharge of 2000 kN of salt water ballast decreases the draft to 6.7 m. What would
be the draft of the ship in fresh water, also with the water ballast pumped out?
(Ans. 6.843 m)
4. A hydrometer has a mass of 10.0 grams and its stem has a cross-sectional area of 16.0 mm2. Calculate
the difference between the depths of floatation in liquids of relative density 1.25 and 0.9.
(Ans. 194 mm)
5. A cylindrical buoy, 2.0 m in diameter and 1.3 m long, floats in sea water with its axis vertical. The
buoy weighs 10.0 kN and its centre of gravity is 0.5 m above the base. If an additional load of 2.0 kN is
to be placed on top of the buoy, find the maximum height of its centre of gravity above the top of the
buoy, so that the buoy may remain in stable equilibrium. You may assume that the mass density of sea
water is 1025 kg/m3.
(Ans. 1.29 m)
CIVN3024A/TTT/2020