Review Exercise 3-2
Section 1: Multiple-Choice
Circle the correct answer (one correct answer for each problem)
Chapter 15: The Laws of Thermodynamics
1. When the first law of
thermodynamics, Q = ΔU + W, is applied to an ideal gas that is taken through an
isothermal process,
A) ΔU = 0
Answer
DU
= 3/2nRDT
= 0
B) W = 0
C) Q = 0
D) none of
the above
2. An ideal gas is compressed to
one-half its original volume during an isothermal process.
The final
pressure of the gas
A) increases
to twice its original value.
Answer
PV = nRT = constant
V/2
ð
Px2
B) increases to
less than twice its original value.
C) increases
to more than twice its original value.
D) does not
change.
3. A gas is quickly compressed
in an isolated environment.
During the event, the gas exchanged no
heat with its surroundings. This
process is
A)
isothermal.
B) isochoric.
C) isobaric.
D) adiabatic.
Answer
4. When the first law of
thermodynamics, Q = ΔU + W, is applied to an ideal gas that is taken through an
isobaric process,
A) ΔU = 0.
B) W = 0.
C) Q = 0.
D) none of
the above
Answer
5. In an isochoric process,
there is no change in
A) pressure.
B)
temperature.
C) volume.
Answer
D) internal
energy.
6) Is it possible to transfer
heat from a cold reservoir to a hot reservoir?
A) No.
B) Yes;
this will happen naturally.
C) Yes,
but work will have to be done.
Answer
D)
Theoretically yes, but it hasn't been accomplished yet.
7) If the theoretical efficiency
of a Carnot engine is to be 100%, the heat sink must be
A) at
absolute zero.
Answer
B) at
0°C.
C) at
100°C.
D)
infinitely hot.
8) According to the second law
of thermodynamics, for any process that may occur within an isolated
system, which one of the choices applies?
A) Entropy
remains constant.
B) Entropy
increases.
C) Entropy
decreases.
D) Both A and
B are possible.
Answer
E) Both A and
C are possible.
Chapter 16: Electric Charge and Electric Field
1. An atom has more electrons
than protons. The atom is
A) a positive
ion.
B) a negative
ion.
Answer
C) a
superconductor.
D)
impossible.
2. Materials in which the
electrons are bound very tightly to the nuclei are referred to as
A)
insulators.
Answer
B)
conductors.
C)
semiconductors.
D)
superconductors.
3. Materials in which the
electrons are bound very loosely to the nuclei and can move about freely within
the material are referred to as
A)
insulators.
B)
conductors.
Answer
C)
semiconductors.
D)
superconductors.
4. Two charged objects are
separated by a distance d. The
first charge is larger in
magnitude
than the second charge.
A) The first
charge exerts a larger force on the second charge.
B) The second
charge exerts a larger force on the first charge.
C) The
charges exert forces on each other equal in magnitude and opposite in
direction.
D) The
charges exert forces on each other equal in magnitude and pointing in the
same direction.
5. Two charged objects attract
each other with a certain force.
If the charges on both objects are
doubled with no change in separation, the force between them
A)
quadruples.
Answer
B) doubles.
C) halves.
D) increases,
but we can't say how much without knowing the distance between them.
6. An electron and a proton are separated by a distance of 1.0 m. What happens to the magnitude of the force on the proton if a second electron is placed next to the
first electron?
A) It
quadruples.
B) It
doubles.
Answer
C) It will
not change.
D) It goes to
zero.
7. An electron and a proton are
separated by a distance of 1.0 m.
What happens to the magnitude of
the force on the first electron if a second electron is placed next to the
proton?
A) It
doubles.
B) It does
not change.
C) It is
reduced to half.
D) It becomes
zero.
Answer
8) An originally neutral
electroscope is briefly touched with a positively charged glass rod.
The
electroscope
A) remains
neutral.
B) becomes
negatively charged.
C) becomes
positively charged.
Answer
D) could
become either positively or negatively charged, depending on the time of
contact.
Section 2: Free Response
Provide answers in the space provided. Follow instructions concerning the
format of each answer as stated in the problem.
1. A gas is enclosed in a cylinder fitted with a light frictionless piston
and maintained at atmospheric
pressure (1.0x105 Pa). When 1.5x102 kcal of heat is
added to the gas, its
volume increases
slowly from 10.0 m3 to 15.0 m3.
You can use the
following approximations: 1 Pa = 1 N/m2.
1 J = 1 Nm, 1 kcal = 4x103
J.
Give exact answers
along with units.
a. What is the work done by
the gas?
Work done
by the gas at constant pressure is given by
W = PDV
= (1.0x105 Pa)(15 m3 - 10m3) = (1x105
N/m2)(5 m3) = 5x105 N m = 5x105
J
b. What is the
change in internal energy of the gas?
DU
= Q - W = (1.5x102 kcal)(4x103 J/kcal) - 5x105
J = 6x105 J - 5x105 J = 1x105 J
2. A heat engine does 1x104 J of work per cycle while absorbing
10.0 kcal of heat from a high-temperature
reservoir. What is the efficiency of this engine? Number required.
The efficiency of a heat engine is e =
W/QH = 1x104 J/(10.0.0 kcal)(kcal/4x103 J)
= 25%
3. What is the
repulsive electrical force between two protons that are 5.0x10-15
m apart from each
other in an atomic nucleus? Use 1.6x10-19 C for the charge of a
proton.
Use k = 9x109
nm2/C2 .Give your answer as an expression with units.
The expression must have all
of the correct values inserted.
F = kQ1Q2/r2
= (9x109 nm2/C2 ) (1.6x10-19
C)(1.6x10-19 C)/ (5.0x10-15 m)2
4. A proton is released in a uniform electric field, and it experiences an electric force of 3.204 x10-14 N toward the south. Use 1.6x10-19 C for the charge of a proton.
What are the magnitude and
direction of the electric field? Do the math - provide a numerical answer with units and
direction.
E = F/q = 3.204x10-14 N south/1.602 x
10-19 C = 2.0x105 N/C south
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5.
Three particles, each with positive charges of +1
mC are located at
the corners of an equilateral triangle of side 1 cm as shown on
the right.
Find the magnitude and direction of the net force on
the particle at the top (number 1). . Use k = 9x109 nm2/C2
.
Show all work and express answer as a number (do the math)
with units. If roots are involved you do not have to evaluate them.
Leave the expression for any roots in your answer. |
 |
F12 = kQ1Q2/1 =
kQ1Q2
F13 = kQ1Q3
=
Since the distances and charges are equal we know
that F12 = F13
From symmetry, we can see that the resultant
vector is pointing straight up, at an angle of 90 degrees from the
horizontal.
Its magnitude is given by F = F12cos(30o)
= (9x109 nm2/C2 ) (1
mC)2(2)1/2/2
F = 4.5x10-3 N
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6. Two balls are shown
on the right. The ball on the left
has a mass (m1) of 2 kg and is travelling to
the
right with a velocity (v1) of 4 m/s. The ball on the
right has a mass (m2) of 4 kg and is travelling
to
the left with a velocity (v2) of 3 m/s. They
collide in a perfectly elastic collision. |
 |
Part a
What conservation law or laws apply?
Conservation of Momentum
Conservation of Kinetic Energy
Part b
What is the velocity of the ball on the left immediately after the
collision? Clearly list the equations that can be solved to find the
velocity. Do not solve the equations, just list them with values inserted
Momentum
is conserved
(m1V1 +
m2V2)initial = (m1V1 + m2V2)final
(2)(4) +
(4)(3) = 20 = 2V1final + 4V2final
10 = V1final
+ 2V2final
Kinetic
Energy is also conserved
1/2(2)(4)2
+ 1/2(4)(3)2 = 16 + 18 = 34
34 =
1/2(2)V12final + 1/2(4)V22final
34 = V12final
+ 2V22final
2
equations in 2 unknowns
10 = V1final
+ 2V2final
34 = V12final
+ 2V22final
Part c
Assume the same situation as above except the collision is inelastic.
Conservation of momentum
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6. A monkey picks a
banana from a tree and then accidentally
drops it
straight down to the bottom of the tree (horizontal line-not
to scale).
He is unstable and angrily picks another banana and
throws it
horizontally with a velocity of 20 m/s. The height above
the ground
at which the throw is made is 45 m (also the distance
straight
down to the first banana).
Ignore air
resistance and assume that the ground is perfectly flat.
For this
problem use g = 10 m/s2 and assume point masses.
How far
from the first banana will the thrown banana land?
Provide a
numerical answer. |
 |
y = y0
+ vy0t + 1/2gt2
y0
= 45 m
y = 0 m
0 = 45 +
0 + 1/2(-10)t2
ð
t2 = 9 t = 3 seconds
before the banana hits the ground.
x = x0
+ vx0t = 0 + 20x3 = 60 m
Section 4
Extra Credit
1. Order or Birth
Place the following
in the order in which they were born. For example, if you believe they
are in the correct
order, then your answer would be A, B, C, D, E
2. Contributions
Identify the
individual above that is being described by placing the letter under his
name on
the line provided.
Parts a, b, and c have one answer each (one person is being described).
Part d requires two
answers (two people are being described).
a. The concept of
the field was developed by him.__________
a
b. His first name
is Robert__________
c
c. The unit for
Joules/coulomb was named after him__________
e
d. Both expressed
an uneasiness with the force at a distance concept__________
b,
d
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3.
Mystery Object |
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I
discussed the object shown on the right a number of
times
in class.
It is
an example of one of the earliest attempts to construct
what
is now called a capacitor. What is it called?
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