Name________________________________Class____________________Date____________________
Assessment
Fluid Mechanics
Teacher Notes and Answers
8 Fluid Mechanics
FLUIDS AND BUOYANT FORCE
10. 2.2  102 N
The metal is more dense than the salt water,
so it is completely submerged. The volume
of the displaced salt water (Vsw) equals the
volume of the metal (Vm).
Given
sw = 1.025  103 kg/m3
l = 1.3 cm
g = 9.81 m/s2
Solution
1. a
2. d
3. a
4. d
5. b
6. c
7. c
8. a
9. Fluids do not possess definite shape,
because the atoms or molecules in the fluid
are free to move past each other. Ice is a
solid in which the water molecules are
bound together in a crystalline arrangement
that prevents their moving past each other.
Ice therefore has a definite shape, and does
not flow. The molecules in liquid water or
steam are able to move past each other, so
that liquid water or steam flows and has no
definite shape, and therefore is a fluid.
Fb = ρ sw
V swg = ρ swV m g = ρ swl 3 g
Fb =(1.025× 10 3 kg/m 3 )(1.3 cm) 3
3
⎛ 1m
⎞
(9.81 m/s 2 )× ⎜
⎜100 cm ⎟
⎟
⎝
⎠
Fb = 2.2× 10 −2 N
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Section Quizzes
Name________________________________Class____________________Date____________________
Assessment
Fluid Mechanics
Section Quiz: Fluids and Buoyant Force
Write the letter of the correct answer in the space provided.
______ 1. Which of the following is a fluid at room temperature?
a. oil
b. wood
c. lead
d. aluminum
______ 2. Which of the following statements is correct?
a. Liquids have a definite shape.
b. Gases have a definite volume.
c. Gases have a definite shape.
d. Liquids have a definite volume.
______ 3. What is true about the volume of displaced fluid for an object that is
completely submerged?
a. The volume of displaced fluid is equal to the object’s volume.
b. The volume of displaced fluid is less than the object’s volume.
c. The volume of displaced fluid is greater than the object’s volume.
d. The volume of displaced fluid is not related to the object’s volume.
______ 4. If an object weighing 50.0 N displaces a volume of water with a weight
of 10.0 N, what is the buoyant force on the object?
a. 60.0 N
b. 50.0 N
c. 40.0 N
d. 10.0 N
______ 5. Which of the following statements is true about the buoyant force on an
object that is floating on the surface of a lake?
a. The buoyant force is greater than the weight of the object.
b. The buoyant force is equal to the weight of the fluid displaced.
c. The buoyant force is the same as when the object is completely
submerged.
d. The buoyant force is less than the density of the water.
______ 6. In which of the following situations will an object sink?
a. The mass density of the object is less than the mass density of the
fluid.
b. The buoyant force on the object is equal to the weight of the object.
c. The mass density of the fluid is less than the mass density of the
object.
d. The weight of the fluid displaced equals the weight of the object.
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Section Quizzes
Name________________________________Class____________________Date____________________
Fluid Mechanics continued
______ 7. An uncooked egg sinks in fresh water but floats in salt water. Which of
the following expressions about the egg’s density (egg) with respect to
the density of fresh water (fw) and the density of salt water (sw) is
correct?
a. egg < fw < sw
c. fw < egg < sw
b. sw < egg < fw
d. fw < sw < egg
______ 8. Which statement about an object placed in water is correct?
a. The apparent weight is always less than the weight of the object in
air.
b. The apparent weight is always equal to the weight of the fluid
displaced.
c. The apparent weight is never equal to zero.
d. The apparent weight is never greater than the buoyant force.
9. Explain why water as ice is not a fluid but water as a liquid or steam is a fluid.
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10. Calculate the buoyant force on a cube of metal with an edge of 1.3 cm that is
placed in salt water. The density of the metal is 7.86  103 kg/m3, and the
density of the salt water is 1.025  103 kg/m3.
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
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Section Quizzes