# CIVE 3434 Lecture 1: Bouyancy(1)

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Buoyancy
1. 2 x 2 x 4 m object is submerged 1.2 m in water. Calculate buoyant force acting on the
object.
Ans.: 47088N
2. A wooden block 3 m x 1.5 m x 2 m with density 600 kg/m3 is floating in water. Will it float
stable along long axis?
Ans.: MG = 0.244 m unstable
3. A rectangular hollow concrete block with a mass of 80 kg must float in river water (1025
kg/m3). The dimensions of a concrete block are 10 m x 5 m x 3 m. Determine whether a
concrete block will float stable along long axis. Take centre of gravity in the centre of the
block. Ans?
4. A loaded pontoon has a mass of 200 000 kg. Its length is 20 m and its width 9 m, and its
overall centre of gravity is 5.6 m above the base of the pontoon. The pontoon floats in
salt water with a density of 1025 kg/m3. Is it stable?
Solution:
Mass of displaced sea water = 200 000 kg
3
122.195
1025
200000 mVol
Depth of immersion
md su b 084.1
920
122.195
mMG
m
V
I
MB
169.16.5
2
084.1
227.6
227.6
122.195
12
920 3
M is above G (6.77 m > 5.6 m) so the pontoon is stable, i.e. MG is positive.
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## Document Summary

Buoyancy: 2 x 2 x 4 m object is submerged 1. 2 m in water. : 47088n: a wooden block 3 m x 1. 5 m x 2 m with density 600 kg/m3 is floating in water. : mg = 0. 244 m unstable: a rectangular hollow concrete block with a mass of 80 kg must float in river water (1025 kg/m3). The dimensions of a concrete block are 10 m x 5 m x 3 m. determine whether a concrete block will float stable along long axis. Take centre of gravity in the centre of the block. Ans: a loaded pontoon has a mass of 200 000 kg. Its length is 20 m and its width 9 m, and its overall centre of gravity is 5. 6 m above the base of the pontoon. The pontoon floats in salt water with a density of 1025 kg/m3. Mass of displaced sea water = 200 000 kg.