Download 0.1 2 = P 2 + 1/2

Chapter 9.1
Review
Fluids
1. What are the
properties of a
fluid? What states
of matter are
fluids?
No definite shape.
The particles are
free to flow around
one another.
Liquids and gases.
2. What is the
volume flow rate
3
3
in m /s if a 2 m
barrel is filled in
2 minutes?
Q = Av
But Q = V/t, also.
3
Q = 2 m / 120 s
3
Q = 0.0167 m / s
3. At the flow rate
found in question 2,
with what speed is
the water leaving a
hose with an area of
-3
2
2.95 x 10 m ?
Q = Av
0.0167 = 2.95 x
v = 5.65 m/s
-3
10
v
4. If the area of the hose in
question 3 was increased to
-3
2
7.35 x 10 m , how does that
affect the flow rate? How
does it affect the speed of the
water leaving the hose?
It doesn’t affect the
volume flow rate at all.
Q = Av
-3
0.0167 = 7.35 x 10 v
v = 2.27 m/s
5. What is
Archimedes’
Principle?
The buoyant
force on a body in
a fluid is equal to
the weight of the
fluid displaced.
6. A 10 N block of
wood floats in
water. What is
the buoyant
force?
10 N, the buoyant
force on a
FLOATING object
is always just its
weight.
7. A person has a volume of
one cubic meter and a
3
density of 925 kg/m . If this
person is in fresh water, will
they float? If so, what volume
of water will they displace?
What volume of “person” is
still above water?
They will float. (Density is
less that the water.)
rVg person = rVg water
rVg = rVg
925(1)10 = 1000 V 10
3
V = 0.925 m
3
1.000 - 0.925 = 0.075 m
8. If the person in
question 7 were in
salt water (density =
3
1025 kg/m ), how
would the answers in
question 7 change?
They would still float.
rVg person = rVg water
rVg = rVg
925(1)10 = 1025 V 10
3
V = 0.902 m
3
1.000 - 0.902 = 0.098 m
6. What is the air
pressure in Pascals
at sea level?
In bars?
In atmospheres?
In Torr?
5
10
1.013 x
Pa
1 bar
1 atmosphere
760 Torr
7. What is the absolute
pressure in Pascals 30
meters below the
surface of fresh water?
What is the gauge
pressure at the same
level?
P2 = P1 + rgh
P2 =
5
10
+ 1000(10)30
P2 = 400000 Pa
gauge pressure is just
rgh, 300000 Pa
8. If the pressure
2
on a 0.025 m area
5
is 3 x 10 Pa, what
is the force on that
surface?
P = F/A, so P x A = F
PxA=F
3x
5
10
Pa x 0.025
7500 N
2
m
=
9. What is
Pascal’s
Principle?
Any change in
pressure anywhere in
a contained fluid is
felt everywhere in the
fluid.
10. A hydraulic system
supports a car with a mass of
1500 kg on a cylinder with an
2
area of 0.8 m . What force
must be applied to a cylinder
2
with an area of 0.1 m to
support the car? What is the
“trade-off” in this situation?
F/A = F/A
2
1500 kg x 10 /0.8 m
2
= F/ 0.1 m
F = 1875 N
The trade is distance to get
force.
11. What is
Bernoulli’s
Principle? Give
one example.
A moving fluid
applies less pressure.
Shower curtain
moving toward you in
the shower.
12. A tube carrying water has an
area of 0.05 m2. The water is
moving at 0.1 m/s and is at a
pressure of 2 x 105 Pa. If the
tube reaches a constriction
where the area becomes
0.01 m2, what is the new velocity
and what is the new pressure?
Av = Av
0.05 x 0.1 = 0.01 x v
v = 0.5 m/s
2
P1 + 1/2 ρv1 + ρgh1 =
2
P2 + 1/2 ρv2 + ρgh2
2 x 105 + 1/2 (1000)0.12 =
2
P2 + 1/2 (1000)0.5
P2 = 199880 Pa
13. Pressure in a water
pipe in an apartment is
5
1.1 x 10 Pa. If the pipe is
vertical, what is the
pressure 8 meters below
the apartment?
P1 + 1/2 ρv1 + ρgh2 =
2
P2 + 1/2 ρv2 + ρgh1
5
1.1 x 10 Pa + 1000(10)8 =
2
P2 = 190000 Pa
14. What is
the ideal gas
law?
PV = nRT
15. One mole of an
ideal gas has a
3
volume of 3 m . If the
temperature is 750 K,
what is the pressure?
PV = nRT
P(3) = 1(8.31)750
P = 2077.5 Pa
16. If the pressure
in problem 15 is
doubled at constant
temperature, what
is the resulting
volume?
PV/T =PV/T
PV = PV
2077.5 x 3 = 4155 x V
3
V = 1.5 m
17. The pressure of a gas is
1 atmosphere and the
temperature is 600 K. If the
temperature is reduced to
300 K without changing the
volume, what is the resulting
pressure?
PV/T =PV/T
P/T = P/T
1/600 = P/300
P = ½ atmospheres