a decrease in temperature and an increase in internal energy.. a decrease in temperature and a decrease in internal energy.. an increase in temperature and an increase in internal energy
Trang 1Time: 30 Minutes
Number of Questions: 30
This test consists of 30 discrete
questions—questions that are NOT based on a descriptive passage These discretes comprise
15 of the 77 questions on the Physical Sciences and Biological Sciences sections of the MCAT
Trang 2MCAT
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PHYSICS DISCRETES TEST DIRECTIONS: The following questions are not
based on a descriptive passage; you must select the best answer to these questions If you are unsure of the best answer, eliminate the choices that you know are incorrect, then select an answer from the choices that remain Indicate your selection by blackening the corresponding circle on your answer sheet A periodic table is provided below for your use with the questions
PERIODIC TABLE OF THE ELEMENTS
1
H
1.0
2
He
4.0 3
Li
6.9
4
Be
9.0
5
B
10.8
6
C
12.0
7
N
14.0
8
O
16.0
9
F
19.0
10
Ne
20.2 11
Na
23.0
12
Mg
24.3
13
Al
27.0
14
Si
28.1
15
P
31.0
16
S
32.1
17
Cl
35.5
18
Ar
39.9 19
K
39.1
20
Ca
40.1
21
Sc
45.0
22
Ti
47.9
23
V
50.9
24
Cr
52.0
25
Mn
54.9
26
Fe
55.8
27
Co
58.9
28
Ni
58.7
29
Cu
63.5
30
Zn
65.4
31
Ga
69.7
32
Ge
72.6
33
As
74.9
34
Se
79.0
35
Br
79.9
36
Kr
83.8 37
Rb
85.5
38
Sr
87.6
39
Y
88.9
40
Zr
91.2
41
Nb
92.9
42
Mo
95.9
43
Tc
(98)
44
Ru
101.1
45
Rh
102.9
46
Pd
106.4
47
Ag
107.9
48
Cd
112.4
49
In
114.8
50
Sn
118.7
51
Sb
121.8
52
Te
127.6
53
I
126.9
54
Xe
131.3 55
Cs
132.9
56
Ba
137.3
57
La *
138.9
72
Hf
178.5
73
Ta
180.9
74
W
183.9
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.1
79
Au
197.0
80
Hg
200.6
81
Tl
204.4
82
Pb
207.2
83
Bi
209.0
84
Po
(209)
85
At
(210)
86
Rn
(222) 87
Fr
(223)
88
Ra
226.0
89
Ac †
227.0
104
Unq
(261)
105
Unp
(262)
106
Unh
(263)
107
Uns
(262)
108
Uno
(265)
109
Une
(267)
*
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0
†
90
Th
232.0
91
Pa
(231)
92
U
238.0
93
Np
(237)
94
Pu
(244)
95
Am
(243)
96
Cm
(247)
97
Bk
(247)
98
Cf
(251)
99
Es
(252)
100
Fm
(257)
101
Md
(258)
102
No
(259)
103
Lr
(260)
Trang 3GO ON TO THE NEXT PAGE.
1 An ideal gas compressed adiabatically
experiences:
A a decrease in temperature and an increase in
internal energy
B a decrease in temperature and a decrease in
internal energy
C an increase in temperature and an increase in
internal energy
D no change in either the temperature or
internal energy
2 Two identical rods having temperatures 100°C
and 50°C, respectively, are brought into contact
If the system is isolated from the environment,
its entropy:
A increases.
B decreases.
C remains the same.
D cannot be determined.
3 A 1.0 kg object moving east with a velocity of
10 m/s has a head-on collision with a 0.5 kg
object which is at rest Neglecting friction, what
is the momentum of the system after collision?
A 15 kg • m/s; east
B 15 kg • m/s; west
C 10 kg • m/s; east
D 10 kg • m/s; west
4 An object is moving counterclockwise in a circle
at constant speed Which of the following diagrams correctly indicates both its velocity vector and its acceleration vector?
v a
A.
v
ar
B.
v
a
C.
v a
D.
at
5 An ambulance originally at rest has its siren
going The ambulance starts accelerating away from a boy standing nearby He will hear:
A a decrease in the pitch of the siren.
B no change in the pitch of the siren.
C an increase in the pitch of the siren.
D an increase, and then a decrease in the pitch
of the siren
Trang 46 The diagram shows energy levels E1, E2, E3, and
E4 in an atom If the transition from energy E3
to E2 gives rise to a photon of radiation of a
particular wavelength, which of the following
transitions could give rise to a photon of
radiation of longer wavelength?
Energy (eV)
E 4
E 3
E 2
E1
A E4 to E1
B E3 to E1
C E2 to El
D E4 to E3
7 The activity of a radioactive source falls to
one-sixteenth of its original value in 32 minutes
What is the half-life, in minutes, of this decay
process?
A 2 min
B 4 min
C 8 min
D 16 min
8 A parallel plate air capacitor is connected across a
battery of constant emf If the separation of the
plates is decreased, which of the following
increases?
I Charge on the plates of the capacitor
II Potential difference between the plates
of the capacitor
III Capacitance of the capacitor
A III only
B I and II only
C I and III only
D II and III only
9 An object (O) is placed within the focal length f
of a converging lens The image (I) is located at which of the following positions?
A.
B.
C.
D.
O
O
f
f' O
O
I I
I
I
1 0 When the 2/3 Ω resistor is replaced by an 8/3 Ω
resistor, the voltage across the resistor changes from:
9 V
2/3 Ω
1/3 Ω
A 4 V to 6 V.
B 4 V to 8 V.
C 6 V to 4 V.
D 6 V to 8 V.
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1 1 From the data shown below, estimate the
half-life of element X
10 x 10 5
7.5 x 10 5
5 x 105
2.5 x 105
0 1.5 3.0 4.5 6.0
Element X
Years elapsed
A 1.5 years
B 3.0 years
C 4.5 years
D 6.0 years
1 2 A planet has a diameter one half of the Earth’s
diameter and a mass that is one half of the
Earth’s mass What would be the acceleration due
to gravity on the planet?
A 2.45 m/s2
B 4.90 m/s2
C 9.80 m/s2
D 19.6 m/s2
1 3 In the diagram below a stream of electrons leaves
the electron gun at G and strikes the fluorescent screen at P When the current is switched on at
S, it flows through the wire coils in an anticlockwise direction as seen by the observer at O; the observer sees the spot of light at P:
S
O
A move downwards.
B move to the left.
C move to the right.
D remain still.
1 4 Object A of mass M is released from height H
while object B of mass 0.5 M is released from height 2H What is the ratio of the velocity of object A to the velocity of object B immediately before they hit the ground? (Note: Assume that air resistance is negligible.)
A 1:1
B 1: 2
C 1:2
D 1:4
Trang 61 5 In the hydraulic lift shown below, piston A has a
cross-sectional diameter of 2 m and piston B a
cross-sectional diameter of 4 m If the force
exerted by piston A on the liquid is doubled, the
force lifting up piston B is:
A
B
A decreased by a factor of 4.
B increased by a factor of 2.
C increased by a factor of 4.
D increased by a factor of 8.
1 6 Which of the following is true of the adiabatic
expansion from point Q to R?
P
V R S
T
Q
V
A The internal energy at Q is greater than at R.
B The internal energy at R is greater than at Q.
C Heat is released by the gas in moving from
Q to R
D Heat is absorbed by the gas in moving from
Q to R
1 7 A fluid flows through a pipe such that the velocity at point A is 1/4 that at point B What
is the ratio of the radius of the pipe at point A to that at point B?
A 1:4
B 2:1
C 4:1
D 1:2
1 8 A cube of wood whose sides are each 10 cm
weighs 16 N in air When half submerged in an unknown liquid it weighs only 10 N What is the density of the liquid? (Note: Assume g = 10 m/s2.)
A 600 kg/m3
B 800 kg/m3
C 1,000 kg/m3
D 1,200 kg/m3
1 9 Two fixed charges of +Q and +3Q repel each
other with a force, F If an additional charge of –2Q is now added to each of the two charges, what is the new force between them?
A Zero
B F/6 attraction
C F/3 repulsion
D F/3 attraction
2 0 If the binding energy of a nucleus is 186.2 MeV,
what is its mass defect? (Note: 1 amu yields 931 MeV of energy, 1 amu is equivalent to 1.66 ×
10–27 kg.)
A 3.3 × 10–28 kg
B 6.6 × 10–28 kg
C 8.3 × 10–27 kg
D 3.1 × 10–25 kg
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2 1 A block starts from rest and slides down along
one quadrant of a frictionless circular track whose
radius is one meter Which of the following is
true?
1 m
A The speed of the block at the bottom will be
the same as if it had fallen vertically
B Mechanical energy will not be conserved.
C The acceleration of the block is constant
throughout the descent
D The total work done by gravity is greater
than if the block had fallen vertically
2 2 Which one of the following is a scalar quantity?
A Velocity
B Force
C Impulse
D Kinetic energy
2 3 A fireboat is fighting a fire to its right but also
has its hoses going full blast into the water to its
left Which law of physics best explains the
reason for this?
A Newton’s law of gravity
B Newton’s second law
C Newton’s third hew
D Conservation of energy
2 4 In a frictionless horizontal mass spring system,
as the mass moves from the point of maximum expansion through the equilibrium position to the point of maximum compression, the potential energy of the system:
A decreases continually
B increases then decreases.
C decreases then increases.
D remains the same.
2 5 Which of the following diagrams accurately
depicts the electric field lines between 2 charges
of equal magnitude but opposite sign?
Trang 8MCAT
2 6 Four positively charged spheres (+1 C each) and
four negatively charged spheres (–1 C each) are
distributed at equally spaced intervals around a
circular hoop whose radius is 1 m as shown
below What is the electrostatic potential at the
center of the hoop? (Note: k is the electrostatic
constant.)
+
+
+ +
–
–
A 0 V
B 4k V
C 8k V
D 16k V
2 7 Which of the following quantities can be
expressed dimensionally as M • L2/T2, where M
is mass, L is length, and T is time?
I Torque
II Work
III Energy
A I only
B I and II only
C II and III only
D I, II, and III
2 8 In an attempt to restore the natural rhythm of a
heart attack victim, electric shock plates are sometimes used The shock plates are run off a
10 V battery and draw current at a constant 30 A
If each shock draws 300 J of electrical energy, what is the duration of the shock?
A 0.1 sec
B 0.3 sec
C 1.0 sec
D 3.0 sec
2 9 A bat locates obstacles in its flight path by
emitting sound in the same direction as it travels When the sound encounters an obstacle, it is reflected back to the bat Assuming that the bat’s velocity and the frequency of the emitted sound are constant, and assuming the obstacle is stationary, which of the following describes the frequency observed by the bat?
A It is greater than the frequency emitted by the
bat
B It is less than the frequency emitted by the
bat
C It is the same as the frequency emitted by the
bat
D Its character cannot be determined.
3 0 An object is moved from 2f towards f, where f is
the focal length of this converging lens The image formed on the other side of the lens will move from:
A f to 2f.
B 2f to f/2.
C 2f to f.
D 2f to infinity.
END OF TEST
Trang 9THE ANSWER KEY IS ON THE NEXT PAGE
Trang 10MCAT
10
ANSWER KEY:
Trang 111 C
This is a first law of thermodynamics question, which states that the change in internal energy, U, equals the heat, Q, minus the work done, W We are asked to find what happens to a gas that is compressed adiabatically
To solvethis problem one must know that adiabatic means that no heat enters or leaves the system This means that
Q is zero, and the first law simplifies to U = –W
Because the system is compressed, work is done on the system, and not by the system Work is therefore negative Another way we could have reached this conclusion from the formula W = PV for an ideal gas Since in this case the final volume is less than its initial volume, V is negative and so is W
Since W is negative, –W is positive and so the change in internal energy is positive Choices B and D can therefore be eliminated Now all that is left is to decide whether an increase in internal energy would increase or decrease the temperature Since temperature increases with the average kinetic energy of the gas molecules, as the internal energy increases, so would the temperature
2 A
In an isolated system, the entropy never decreases The only possibilities are entropy remains the same (if the process is reversible) or it increases (if the process is irreversible) Under what category does this process fall?
When the two rods are put in thermal contact, heat will flow from the hot rod to the cold one until both rods are at the same temperature (in thermal equilibrium) Is it possible for the original situation (hot rod/cold rod) to redevelop spontaneously? No: the process is irreversible The answer is thus choice A
Note that the rod that is hot originally will experience a decrease in entropy as it cools This rod by itself is however not an isolated system (energy is flowing out of it into the cold rod) and therefore it doesn’t violate what we have just said The increase in entropy of the cold hot upon warming is larger in magnitude than the decrease in entropy of the hot rod as it cools, thus leading to a net increase in entropy
3 C
The two concepts necessary to keep in mnd to solve this problem are (1) momentum is conserved in a collision and (2) momentum is the product of mass and velocity Conservation of momentum states that the momentum immediately before a collision equals the momentum immediately after the collision Before the collision, the 1.0-kg object has a momentum of 1.0 kg × 10 m/s = 10 kg•m/s This is the total initial momentum since the other object is at rest (v = 0, hence p = mv = 0) This initial momentum of the system points in the same direction as the velocity of the moving object, i.e towards the east This must then also be the momentum of the system after collision
4 A
The object is undergoing uniform circular motion as its trajectory is circular and it is moving at a constant speed The velocity of the object is always tangential to the circle On this criterion alone, choices B and C can be eliminated For uniform circular motion, there is no tangential component to the acceleration The acceleration is therefore entirely radial and is called the centripetal acceleration, with magnitude equal to v2/r It points towards the center of the circle
5 A
This is a Doppler effect question where we have a source moving away from a stationary observer The exact form of the equation that describes this situation is:
f’ = fv (v + vs)
where f’ is the observed frequency, f is the actual frequency (from the point of view of the source), v the velocity of sound in the medium, and vs the velocity of the source We do not need to remember this equation specifically though to answer the question (In fact it is very unlikely that the MCAT will expect you to have memorized this.)
We should, however, be able to reason out that if the source is constantly moving away from the observer, successive wave crests would take longer and longer to reach the observer, leading to a perception of a lower frequency or pitch The faster the source is moving away, the lower the perceived pitch would be Here the ambulance is accelerating from the boy; its speed is therefore increasing The pitch would then be decreasing
6 D