Plate No.6 - Solution
Plate No.6 - Solution
Plate No.6 - Solution
2. ℎ = 0.917 ft
3. 𝜃 = 19.471°
4. 𝐹 = 19.62 kN
1
𝑦= 2 = 0.667 m
3
𝑉𝑐𝑜𝑛𝑐 = 0.316 m3
𝑃𝑅𝑂𝐵𝐿𝐸𝑀 1
A hollow cylinder 1m in diameter and 2 m high weighs 3825 N.
(a) How many kN of lead weighing 110 kN/m3 must be fastened to the outside bottom of the cylinder to make it
float with 1.5 m submerged in water?
(b) How many kN of lead if it is placed inside the cylinder?
Solution
1m
(a) Lead is fastened outside (b) Lead is fastened inside the cylinder
𝐵𝐹𝐶 = 𝛾𝑤𝑉𝐷 0.5 m WC [Σ𝐹𝑉 = 0] 1m
𝐵𝐹𝐶 = 9.81(𝜋/4)(12)(1.5) 𝐵𝐹 = 𝑊𝐶 + 𝑊𝐿
2m
𝐵𝐹𝐶 = 11.557 kN 1.5 m 11.557 = 3.825 + 𝑊𝐿 0.5 m WC
BFC
𝑊𝐿 = 7.732 kN
2m
𝐵𝐹𝐿 = 𝛾𝑤𝑉𝐿 1.5 m
𝐵𝐹𝐿 = 9.81𝑉𝐿
WL
𝑊𝐿 = 𝛾𝑤𝑉𝐿 = 110𝑉𝐿
WL
BFL
[Σ𝐹𝑉 = 0] BF
𝐵𝐹𝐶 + 𝐵𝐹𝐿 = 𝑊𝐶 + 𝑊𝐿
11.557 + 9.81𝑉𝐿 = 3.825 + 110𝑉𝐿
𝑉𝐿 = 0.077 m3
𝑊𝐿 = 8.489 kN
𝑃𝑅𝑂𝐵𝐿𝐸𝑀 2
A cube 2.2 ft on an edge has its lower on an edge has its lower half of sg = 1.6 and upper half of sg = 0.7. It rests
in a two-layer fluid, with lower sg = 1.4 and upper sg = 0.8. Determine the height h of the top of the cube above
the interface.
Solution
sg = 0.8
𝐵𝐹 = 62.4 × 1.4 2.2 2 2.2 − ℎ + 62.4 × 0.8 [ 2.2 2 ℎ ]
𝐵𝐹 = 62.4 × 2.22 (3.08 − 1.4ℎ + 0.8ℎ)
sg = 0.7
𝑊 = 62.4 × 1.6 [ 2.2 2 1.1 ] + 62.4 × 0.7 [ 2.2 2 1.1 ] h
𝑊 = 62.4 × 2.22 (2.53) 2.2 ft
sg = 1.6
𝐵𝐹 = 𝑊
62.4 × 2.22 (3.08 − 1.4ℎ + 0.8ℎ) = 62.4 × 2.22 (2.53)
sg = 1.4 2.2 ft
ℎ = 0.917 ft
𝑃𝑅𝑂𝐵𝐿𝐸𝑀 3
A wooden beam of specific gravity 0.64 is 150 mm by 150 mm and is hinged at A, as shown in the figure. At what
angle ϴ will the beam float in water?
Solution
A
𝑊 = 𝛾𝑏𝑒𝑎𝑚𝑉𝑏𝑒𝑎𝑚
𝑊 = 9810 × 0.64 0.15 × 0.15 × 5 = 706.32 N
1m
𝐵𝐹 = 𝛾𝑤𝑉𝐷
𝐵𝐹 = 9810 0.15 × 0.15 × 𝑥 = 220.725𝑥 N ϴ
Water
Σ𝑀𝐴 = 0
𝑥
𝐵𝐹 + 5−𝑥 cos 𝜃 − 𝑊(2.5 cos 𝜃) = 0
2
𝑥 A
𝐵𝐹 + 5−𝑥 cos 𝜃 = 𝑊(2.5 cos 𝜃)
2
𝑥
220.725𝑥 + 5−𝑥 = 706.32(2.5) 1m
2
𝑥 =2m ϴ
1 1 Water
sin 𝜃 = = 𝜃 = 19.471°
5−𝑥 5−2 W
BF
𝑃𝑅𝑂𝐵𝐿𝐸𝑀 4
From the figure below, it is shown that the gate is 1.0 m wide and is hinge at the bottom of the gate. Compute the
following:
(a) the hydrostatic force in kN acting on the gate
(b) the location of the center of pressure of the gate from the hinge,
(c) the minimum volume of concrete (unit weight = 23.6 kN/m3) needed to keep the gate closed position.
Solution
Pulley
ത = 9.81(1)(2 × 1)
𝐹 = 𝛾ℎ𝐴
𝐹 = 19.62 kN
1m
1
𝑦 = 2 = 0.667 m T
3
W Submerged
Σ𝑀𝐴 = 0 Σ𝐹𝑦 = 0 concrete
𝐹𝑦 = 𝑇(3) 𝑇 + 𝐵𝐹 = 𝑊 2m block