Fluid Mechanics and Heat Study guide
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
____
1. Which of the following is a fluid?
a. helium
b. ice
c. iron
d. gold
2. Which of the following is not a fluid?
a. carbon dioxide
b. hydrogen
c. seawater
d. wood
____
3. Which of the following statements is not correct?
a. A fluid flows.
b. A fluid has a definite shape.
c. Molecules of a fluid are free to move past each other.
d. A fluid changes its shape easily.
____
4. How does a liquid differ from a gas?
a. A liquid has both definite shape and definite volume, whereas a gas has neither.
b. A liquid has definite volume, unlike a gas.
c. A liquid has definite shape, unlike a gas.
d. A liquid has definite shape, whereas a gas has definite volume.
____
5. When a gas is poured out of one container into another container, which of the following does not occur?
a. The gas flows into the new container.
b. The gas changes shape to fit the new container.
c. The gas spreads out to fill the new container.
d. The gas keeps its original volume.
____
6. For incompressible fluids, density changes little with changes in
a. depth.
c. pressure.
b. temperature.
d. free-fall acceleration.
____
7. A buoyant force acts in the opposite direction of gravity. Therefore, which of the following is true of an object
completely submerged in water?
a. The net force on the object is smaller than the weight of the object.
b. The net force on the object is larger than the weight of the object.
c. The net force on the object is equal to the weight of the object.
d. The object appears to weigh more than it does in air.
____
8. Which of the following statements about floating objects is correct?
a. The object’s density is greater than the density of the fluid on which it floats.
b. The object’s density is equal to the density of the fluid on which it floats.
c. The displaced volume of fluid is greater than the volume of the object.
d. The buoyant force equals the object’s weight.
____
9. Which of the following statements about completely submerged objects resting on the ocean bottom is
correct?
a. The buoyant force acting on the object is equal to the object’s weight.
b. The apparent weight of the object depends on the object’s density.
c. The displaced volume of fluid is greater than the volume of the object.
d. The weight of the object and the buoyant force are equal and opposite.
____ 10. If an object is only partially submerged in a fluid, which of the following is true?
a. The volume of the displaced fluid equals the volume of the object.
b. The density of the fluid equals the density of the object.
c. The density of the fluid is greater than the density of the object.
d. The density of the fluid is less than the density of the object.
____ 11. Which of the following is not an example of units for expressing pressure?
a. N/m
c. atm
b. kg/m
d. Pa
____ 12. Which of the following statements is true according to Pascal’s principle?
a. Pressure in a fluid is greatest at the walls of the container holding the fluid.
b. Pressure in a fluid is greatest at the center of the fluid.
c. Pressure in a fluid is the same throughout the fluid.
d. Pressure in a fluid is greatest at the top of the fluid.
____ 13. Which of the following statements is always true?
a. Pressure always increases when force increases or the area acted on increases.
b. Pressure always increases when force increases or the area acted on decreases.
c. Pressure always increases when force decreases or the area acted on increases.
d. Pressure always increases when force decreases or the area acted on decreases.
____ 14. What factors affect the gauge pressure within a fluid?
a. fluid density, depth, free-fall acceleration
b. fluid volume, depth, free-fall acceleration
c. fluid mass, depth, free-fall acceleration
d. fluid weight, depth, free-fall acceleration
____ 15. What does the difference between gauge pressure and absolute pressure equal?
a. the pressure within the fluid
c. the pressure at the bottom of the fluid
b. the pressure at the surface of the fluid
d. zero
____ 16. What does the net force between two levels in a fluid equal?
a. the weight of the fluid above the top level
b. the weight of the fluid between the levels
c. the force applied to the fluid’s surface
d. the force applied to the fluid’s sides
____ 17. Which of the following properties is not characteristic of an ideal fluid?
a. laminar flow
c. nonviscous
b. turbulent flow
d. incompressible
____ 18. Which of the following is not an example of laminar flow?
a. a river moving slowly in a straight line
b. smoke rising upward in a smooth column through air
c. water flowing evenly from a slightly opened faucet
d. smoke twisting as it moves upward from a fire
____ 19. Which of the following is not an example of turbulent flow?
a. a river flowing slowly in a straight line
b. a river flowing swiftly around rocks in rapids
c. water flowing unevenly from a fully opened faucet
d. smoke twisting as it moves upward from a fire
____ 20. An ideal fluid flows through a pipe made of two sections with diameters of 1 cm and 3 cm, respectively. By
what factor would you have to multiply the velocity of the liquid flowing through the 1 cm section to obtain
the velocity of liquid flowing through the 3 cm section?
a. 9
c.
b. 6
d.
____ 21. Why does an ideal fluid move faster through a pipe with decreasing diameter?
a. The pressure within the fluid increases.
b. The pressure within the fluid decreases.
c. The pipe exerts more pressure on the fluid.
d. The fluid moves downhill.
____ 22. Why does the lift on an airplane wing increase as the speed of the airplane increases?
a. The pressure behind the wing becomes less than the pressure in front of the wing.
b. The pressure behind the wing becomes greater than the pressure in front of the wing.
c. The pressure above the wing becomes less than the pressure below the wing.
d. The pressure above the wing becomes greater than the pressure below the wing.
____ 23. For an ideal fluid flowing through a horizontal pipe, Bernoulli’s principle and the continuity equation state
that the pressure within the pipe does which of the following? (Assume measurements are taken along the
pipe in the direction of fluid flow.)
a. Pressure increases as the pipe diameter increases.
b. Pressure decreases as the pipe diameter increases.
c. Pressure remains constant as the pipe diameter increases.
d. Pressure increases, then decreases as the pipe diameter increases.
____ 24. Which of the following occurs to a person standing near the edge of a railroad track when a high-speed train
passes?
a. The person tends to be pushed away from the train.
b. The person tends to be pulled toward the train.
c. The person tends to be pushed upward into the air.
d. The person is unaffected by the train.
____ 25. What happens when a person blows between two paper cups that are hung by strings 10 cm apart?
a. The cups move toward each other.
c. The cups do not move.
b. The cups move away from each other.
d. The cups move upward.
____ 26. Which of the following is a direct cause of a substance’s temperature increase?
a. Energy is removed from the particles of the substance.
b. Kinetic energy is added to the particles of the substance.
c. The number of atoms and molecules in a substance changes.
d. The volume of the substance decreases.
____ 27. What happens to the internal energy of an ideal gas when it is heated from 0C to 4C?
a. It increases.
c. It remains constant.
b. It decreases.
d. It is impossible to determine.
____ 28. Which of the following is proportional to the kinetic energy of atoms and molecules?
a. elastic energy
c. potential energy
b. temperature
d. thermal equilibrium
____ 29. Which of the following is a form of kinetic energy that occurs within a molecule when the bonds are stretched
or bent?
a. translational
c. vibrational
b. rotational
d. internal
____ 30. What are the energies associated with atomic motion called?
a. kinetic energy
c. bond energy
b. potential energy
d. internal energy
____ 31. Which of the following best describes the relationship between two systems in thermal equilibrium?
a. No net energy is exchanged.
c. The masses are equal.
b. The volumes are equal.
d. The velocity is zero.
____ 32. As the temperature of a substance increases, its volume tends to increase due to
a. thermal equilibrium.
c. thermal expansion.
b. thermal energy.
d. thermal contraction.
____ 33. What is the temperature of a system in thermal equilibrium with another system made up of water and steam
at 1 atm of pressure?
a. 0°F
c. 0 K
b. 273 K
d. 100C
____ 34. What is the temperature of a system in thermal equilibrium with another system made up of ice and water at 1
atm of pressure?
a. 0°F
c. 0 K
b. 273 K
d. 100C
____ 35. If two small beakers of water, one at 70C and one at 80C, are emptied into a large beaker, what is the final
temperature of the water?
a. The final temperature is less than 70C.
b. The final temperature is greater than 80C.
c. The final temperature is between 70C and 80C.
d. The water temperature will fluctuate.
____ 36. Which of the following is not a widely used temperature scale?
a. Kelvin
c. Celsius
b. Fahrenheit
d. Joule
____ 37. What temperature has the same numerical value on both the Fahrenheit and the Celsius scales?
a. –40.0
c. 40.0
b. 0
d. –72.0
Problem
38. An air-filled balloon with a mass of 3.3 g is placed in a pool of water. What is the magnitude of the buoyant
force acting on the balloon if the density of air is 1.29 10 g/cm and the density of water is 1.00 g/cm ?
39. An ice cube is placed in a glass of water. The cube is 2.1 cm on each side and has a density of 0.919 g/cm .
What is the magnitude of the buoyant force on the ice?
40. A raft with a length of 8.0 m, a width of 1.6 m, a thickness of 0.11 m, and a density of 690.0 kg/m is placed
in a river. How far below the water’s surface does the bottom of the raft sink? (Recall that fresh water has a
density of 1.00 10 kg/m .)
41. A block of wood has a density of 0.820 g/cm and dimensions of 19.0 cm, 9.0 cm, and 4.0 cm. How large a
force will just submerge the block in a vat of oil with a density 0.920 g/cm ?
42. A ball with a density of 0.930 g/cm and a volume of 1.5 10 cm is placed in a fluid with a density of
0.830 g/cm . Does the ball sink or float? If the ball floats, calculate the volume of the displaced fluid. If the
ball sinks, calculate the magnitude of the apparent weight of the ball.
43. A table-tennis ball has an average density of 0.084 g/cm and a diameter of 4.0 cm. How large a force can just
submerge the ball in water? ( = 1.000 g/cm )
44. A piece of wood with a mass of 8.71 kg is placed in fresh water ( = 1.00 g/cm ). What is the density of the
wood if it has an apparent weight of –5.77 ?
45. A ship floats 0.186 m higher when in sea water than it does in fresh water. Given the densities of sea water
( = 1.0250 g/cm ) and fresh water ( = 1.0000 g/cm ), determine how much of the ship’s hull lies
beneath the surface of both kinds of water.
46. A submersible with a mass of 2.78  10 kg remains at a constant depth beneath the ocean surface. To make
the submersible rise, 1.97  10 kg of ballast is released. Ignoring friction, what is the upward acceleration of
the submersible? ( = 1.025  10 kg/m )
47. A 0.330 kg ball is held 2.8 m under water. When the ball is released, it rises with a constant acceleration and
reaches the surface with a speed of 0.74 m/s. Ignoring friction between the ball and the water, what is the
density of the ball? ( = 1.00  10 kg/m )
48. A spherical, helium-filled balloon with a radius of 20.7 cm floats upward in air, but is held in place by a
thread attached to a spring, which is stretched until the balloon rises no further. If the density of helium is
0.18  10 g/cm and the density of air is 1.29  10 g/cm , how large is the force exerted by the spring?
Assume that the balloon material, thread, and spring have negligible masses.
49. A cubical block of wood with a volume of 1.77  10 cm floats on the surface of water ( = 1.00 g/cm ).
Oil ( = 0.60 g/cm ) is poured over the block until it is completely covered. If 6.4 cm of the block’s vertical
side lies below the water’s surface, what is the mass of the block?
50. A hydraulic lift consists of two pistons that connect to each other by an incompressible fluid. If one piston has
an area of 0.49 m and the other an area of 6.2 m , how large a mass can be raised by a force of 220 N
exerted on the smaller piston?
51. A hydraulic lift consists of two cylindrical pistons, one with a radius of 1.9 m and the other with a radius of
0.11 m. While the mass of the smaller piston is negligible, the mass of the larger piston is 6.80  10 kg.
What force must be applied to the smaller piston if a crate with a mass of 1.23  10 kg is to be raised on the
larger piston?
52. A hydraulic lift with pistons of radius 49 cm and 2.5 m is used to lift a mass of 6.4  10 kg a distance of 3.2
m above the ground. How far must the smaller piston be pushed to accomplish this? Assume that both pistons
and the incompressible fluid have negligible mass.
53. Assuming atmospheric pressure to be 1.01  10 Pa and the density of sea water to be 1025 kg/m , what is
the absolute pressure at a depth of 35.6 m below the surface of the ocean?
54. The absolute pressure below the surface of a freshwater lake is 2.43  10 Pa. At what depth does this
pressure occur? Assume that atmospheric pressure is 1.01  10 Pa and that the density of the water is 1.00 
10 kg/m .
55. A mercury barometer consists of a glass column from which air has been removed so that there is negligible
pressure above the mercury column. The pressure on mercury in a reservoir pushes the mercury into the
column until the weight of the mercury equals the force exerted by the air. How high does the mercury ( =
13.6  10 kg/m ) rise when atmospheric pressure is 0.925  10 Pa?
56. A circular hatch in the hull of a submarine has a radius of 51.2 cm. The submarine is 451.4 m under water. If
atmospheric pressure above the ocean is 1.01  10 Pa and the air pressure inside the submarine is 1.34  10
Pa, what net force is exerted on the hatch? ( = 1025 kg/m )
57. Water flows at a speed of 13 m/s through a pipe that has a radius of 0.77 m. The water then flows through a
smaller pipe at a speed of 46 m/s. What is the radius of the smaller pipe?
58. Water in a hypodermic syringe moves from the barrel of the syringe, which has a cross-sectional area of 0.35
cm , to the needle of the syringe, which has a cross-sectional area of 1.3  10 cm . If the water moves
through the barrel at a speed of 0.32 cm/s, what is the speed with which the water leaves the needle?
59. A warm day has a high temperature of 38.1C. What is this temperature in degrees Fahrenheit?
60. The temperature of an object is measured as 489.5 K. What is this temperature in degrees Celsius?
61. What temperature on the Celsius scale is the equivalent of 87.3F?
62. Liquid oxygen has a temperature of –189C. What is this temperature in kelvins?
63. The temperature of an oxygen tank is at 279 K, and the temperature of a nitrogen tank is 15C. How much
greater is the temperature of the nitrogen tank? (Express the answer in kelvins.)
64. The body temperature of a certain human being is 98.27F. What does this temperature equal in kelvins?
65. The surface temperature of Venus is 737 K. What is this temperature in degrees Fahrenheit?
Fluid Mechanics and Heat Study guide
Answer Section
Given
T =T 
Solution
PTS: 1
DIF: IIIB
OBJ: 9-1.3
DIF: IIIA
OBJ: 8-1.3
PROBLEM
38. ANS:
3.2 10
N
Given
Solution
For a floating object,
PTS: 1
39. ANS:
8.3 10 N
Given
 = 0.919 g/cm
= 2.1 cm
g = 9.81 m/s
Solution
The ice floats, so
PTS: 1
40. ANS:
0.076 m, or 7.6 cm
DIF: IIIA
OBJ: 8-1.3
Given
Solution
The raft floats, so
The volume of the displaced fluid is equal to the area of the raft times the distance y that the raft sinks into the
water.
PTS: 1
41. ANS:
0.67 N
DIF: IIIB
OBJ: 8-1.3
Given
 = 0.820 g/cm
= 19.0 cm
w = 9.0 cm
t = 4.0 cm
 = 0.920 g/cm
g = 9.81 m/s
Solution
The applied force, when added to the weight of the block, must be equal and opposite the buoyant force on
the block.
PTS: 1
DIF: IIIB
OBJ: 8-1.3
42. ANS:
The ball sinks; its apparent weight has a magnitude of 15 N.
Given
 = 0.930 g/cm
V = 1.5  10 cm
 = 0.830 g/cm
g = 9.81 m/s
Solution
PTS: 1
43. ANS:
0.30 N
DIF: IIIB
OBJ: 8-1.3
Given
 = 0.084 g/cm
diameter = 4.0 cm
 = 1.000 g/cm
g = 9.81 m/s
Solution
The applied force, when added to the weight of the ball, must be equal and opposite the buoyant force on the
ball.
PTS: 1
44. ANS:
1.07 g/cm
Given
m = 8.71 kg
 = 1.00 g/cm
F = –5.77 N
g = 9.81 m/s
Solution
DIF: IIIB
OBJ: 8-1.3
The weight of the wood is greater than the buoyant force, so the block is submerged, and therefore the volume
of the displaced water equals the volume of the block. The density of the wood is equal to its mass over the
volume of the displaced water.
PTS: 1
DIF: IIIB
OBJ: 8-1.3
45. ANS:
7.63 m in fresh water; 7.44 m in sea water
Given
y –y
= 0.186 m

= 1.0250 g/cm

= 1.0000 g/cm
Solution
The ship floats in both situations, so
Assuming the volume of the displaced water equals the depth of the ship in the water multiplied by a given
area A,
PTS: 1
46. ANS:
0.695 m/s
DIF: IIIC
OBJ: 8-1.3
Given
m = 2.78  10 kg
m = 1.97  10 kg
g = 9.81 m/s
Solution
Before releasing the ballast, the submersible’s total weight (m g ) equals the buoyant force (F ). When the
ballast is released, the net force on the submersible is therefore
PTS: 1
47. ANS:
991 kg/m
Given
m = 0.330 kg
y = 2.8 m
v = 0 m/s
v = 0.74 m/s
 = 1.00  10 kg/m
g = 9.81 m/s
Solution
DIF: IIIC
OBJ: 8-1.3
Calculate the net acceleration of the ball from the information on its speed and the distance traveled.
PTS: 1
48. ANS:
0.405 N
Given
r = 20.7 cm
 = 0.18  10
 = 1.29  10
DIF: IIIC
OBJ: 8-1.3
g/cm
g/cm
g = 9.81 m/s
Solution
The balloon is effectively submerged in the air, so V = V .
The net force raising the balloon is equal to the force exerted by the spring holding the balloon in place.
PTS: 1
49. ANS:
1.5 kg
DIF: IIIC
OBJ: 8-1.3
Given
V =
r = 1.00 g/cm
r = 0.60 g/cm
y = 6.4 cm
Solution
Because the block is a cube, each side has the same length.
The submerged block floats because of buoyant forces from both the water and the oil. The volume in the
water is the area of the cube ( ) that is submerged multiplied by the amount of its vertical side that lies
under water (y). The remainder of the volume is in the oil.
PTS: 1
50. ANS:
280 kg
Given
A = 0.49 m
A = 6.2 m
F = 220 N
g = 9.81 m/s
DIF: IIIC
OBJ: 8-1.3
Solution
PTS: 1
51. ANS:
63 N
DIF: IIIA
OBJ: 8-2.1
DIF: IIIB
OBJ: 8-2.1
Given
r = 1.9 m
r = 0.11 m
m
= 6.80  10 kg
m = 1.23  10 kg
g = 9.81 m/s
Solution
PTS: 1
52. ANS:
84 m
Given
r = 49 cm
r = 2.5 m
m = 6.4  10 kg
d = 3.2 m
g = 9.81 m/s
Solution
Work is conserved, so the force exerted through a distance on one side of the lift equals the force through a
distance on the other side.
PTS: 1
53. ANS:
4.59  10 Pa
DIF: IIIC
OBJ: 8-2.1
DIF: IIIA
OBJ: 8-2.2
Given
P = 1.01  10 Pa
 = 1025 kg/m
h = 35.6 m
g = 9.81 m/s
Solution
PTS: 1
54. ANS:
14.5 m
Given
P = 2.43  10 Pa
P = 1.01  10 Pa
 = 1.00  10 kg/m
g = 9.81 m/s
Solution
PTS: 1
55. ANS:
0.693 m
DIF: IIIA
OBJ: 8-2.2
Given
P = 0.925  10 Pa
P = 0 Pa

= 13.6  10 kg/m
g = 9.81 m/s
Solution
PTS: 1
56. ANS:
3.71  10 N
DIF: IIIB
OBJ: 8-2.2
Given
r = 51.2 cm
h = 451.4 m
P = 1.01  10 Pa
P = 1.34  10 Pa
 = 1025 kg/m
g = 9.81 m/s
Solution
The pressure exerted on the hatch by the sea water and atmosphere above it is
The net force on the hatch equals the net pressure multiplied by the area of the hatch.
PTS: 1
57. ANS:
0.41 m
DIF: IIIC
OBJ: 8-2.2
PTS: 1
DIF: IIIA
58. ANS:
860 cm/s, or 8.6 m/s
OBJ: 8-3.1
Given
v = 13 m/s
r = 0.77 m
v = 46 m/s
Solution
Given
A = 0.35 cm
A = 1.3  10 cm
v = 0.32 cm/s
Solution
PTS: 1
59. ANS:
100.6F
DIF: IIIA
OBJ: 8-3.1
DIF: IIIA
OBJ: 9-1.3
DIF: IIIA
OBJ: 9-1.3
DIF: IIIA
OBJ: 9-1.3
Given
T = 38.1C
Solution
PTS: 1
60. ANS:
216.4C
Given
T = 489.5 K
Solution
PTS: 1
61. ANS:
30.7C
Given
T = 87.3F
Solution
PTS: 1
62. ANS:
84 K
Given
T = –189C
Solution
PTS: 1
63. ANS:
9K
Given
T
T
DIF: IIIA
OBJ: 9-1.3
DIF: IIIB
OBJ: 9-1.3
DIF: IIIB
OBJ: 9-1.3
DIF: IIIB
OBJ: 9-1.3
= 15C
= 279 K
Solution
PTS: 1
64. ANS:
309.97 K
Given
T = 98.27F
Solution
PTS: 1
65. ANS:
867F
Given
T = 737 K
Solution
PTS: 1