Physics B Section 1 Time 90 minutes 70 Questions
Directions: Each of the questions or incomplete statements below is followed by five suggested
answers or completions. Select the one that is best in each case and then fill in the
corresponding oval on the answer sheet.
Note: To simplify calculations, you may use g=10 m/s2 in all problems.
31. A solid metal ball and a hollow plastic ball of the same external radius are released from rest in a
large vacuum chamber. When each has fallen 1 m they both have the same
mass dependent
(A) inertia
(D) kinetic energy
KE=1/2 mv2 (mass dependent)
32.
p=mv ( mass dependent)
(B) speed
(C) momentum
(E) change in potential energy
GPE = mgh ( mass dependent)
A student having a mass of 70 kg starts at rest and accelerates to 3.0 m/s in .50 seconds. What
is the rating of this student? P =  KE / time = ½ mv2 / t = ½ (70kg)(3.0m/s-0m/s)2/.50s=
(A) 315 W
(D) 2100 W
33.
½ mv2=mgh ( mass independent)
(B) 420 W
(E) 1260 W
(C) 630 W
A railroad car of mass M is moving at speed v when if collides with a second railroad car of
mass m which is at rest. The two cars lock together instantaneously and move along the track.
What is the speed of the cars immediately after the collision?
p = po Mv=(M+m)V
Mv / ( M+m) = V
(A) v
2
(B) Mv
m
(D) m v
(M +m)
(E)
(C) mv
M
Mv
(m+M )
34.
An open cart on a level surface is rolling without frictional on a level track and loses water through a
hole in the bottom of a cart. The velocity of the cart will
(A) increase because of conservation of momentum
(B) increase because of conservation of mechanical energy
(C) decrease because of conservation of momentum
(D) decrease because of conservation of mechanical energy
(E) remain the same because the momentum of the system remains the same.
The water leaves with its momentum mwater v
(mcart + mwater) vcartwater = mcart v + mwater v
35.
Units of power include which of the following
I. N m/s
II. Joule per second
III. Kg m2/s2
(A) I only
(B) III only
(C) I and II only
(D) II and III only
(E) I, II, and III
36.
P = F v = N m/s = kg m/s2 m/s = kg m2 / s3
P = Work / time = J / s =
Three forces act on an object. If the object is in translational equilibrium, which of the
following is true?
I.
The vector sum of the three forces must equal zero. (Defines equilibrium )
II.
The magnitudes of the three forces must be equal ( Does not need to be )
III.
All three forces must be parallel.(Does need to be )
(A) I only
(B) II only
(C) I and III only
(D) II and III only
(E) I, II, and III
37.
A child pushes on a box of mass m which moves with constant speed v up an incline
The coefficient of friction between the box and the floor is . At what rate does the child do
work on the box?
Work = F d = (Fgparallel + Ffr)d
Work/ time = (Fgparallel + Ffr)d / t
Work/time=(Fgparallel + Ffr) v
Work time =  mgsin m g cos  ) v
 mgsin m g cos  ) v (B)  mgsin m g cos  )v
(D) mg cos  / v
38.
(E) 
(C) v /
g cos 
g sin  v2
An object has a weight W when it is on the surface of planet R. What will be the gravitational
force on the object it has been moved to a distance of 4R from the center of the planet?
A) 16 W
(B) 4W C) W D) 1/4 W E) 1/16 W
Fg =G mm
The Weight of an object is therefore inversely related to the square of R
r2
39. This graph represents the potential energy U as a function of displacement x for an object on the
end of a spring oscillating in simple harmonic motion with amplitude xo. Which of the following
graphs represents the kinetic energy K of the object as a function of displacement?
U
-xo
O
Us + K = 0
As Us decreases
K will increase
xo
K
(A)
(B)
-xo
O
xo
D)
K
-xo
(C)
O
xo
K
-xo
O
xo
(E)
K
-xo
O
K
xo
-xo
O
xo
40. What is the kinetic energy of a satellite of mass m that orbits the Earth, of mass M, in a circular
orbit of radius R?
(A)
zero
KE=1/2 mv2
(B) 1/2 GMm
R
Fg = Fc GmM = mv2
R2
R
C) GMm
R
GM = v
R
D) GMm
R2
KE = ½ m(
E) ½ GMm
R2
GM )2= ½ mG M
R
R
0.2 kg
0.1 kg
41.. Two objects of mass 0.2 kg and 0.1 kg respectively, move parallel to the x-axis, as shown above.
The 0.2kg object overtakes and collides with the 0.1kg object. Immediately after the collision, the y
component of the velocity of the 0.1 kg object is 2 m/s downward What is the y-component of the
velocity of the 0.2 kg object immediately after the collision?
(A) 1 m/s upward
(B) .5 m/s upward
(C) 0 m/s
(D) .5 m/s downward
(E) 1 m/s downward
poy = py = 0
.2kg ( vy) + .1kg ( -2m/s) = 0
vy =+1m/s
Questions 42 and 43
Three objects can move along a straight, level path. The graphs below show the position d of each of
the objects plotted as a function of time t.
d
d
t
I
42.
(A)
(D)
P= mv
Since this object is
decelerating its velocity is
decreasing ( decreasing slope)
its momentum also decreases
d
t
II
t
III
The magnitude of the momentum is decreasing in which of the cases?
II only
(B)
III only
(C) I and II only
I and III only
(D)
I, II, and III
43. The sum of the forces on the object is zero in which of the cases?
(A)
II only
(B)
III only
(C)
I and II only
(D)
I and III only
(E)
I, II, and III
the objects in I and II are moving at a constant velocity therefore
the net force is zero
44.
A ball of mass 0.40kg is moving at 2.0 m/s and is pushed from behind and obtains a speed of
5.0 m/s. The magnitude of the impulse imparted on the ball is most nearly
(A) 0.8 N* s
impulse = change in momentum =  mv = .40kg ( 5.0m/s – 2.0m/s) = 1.2kgm/s
(B) 1.2 N* s N s = kg m s = kg m/s
(C) 2.0 N* s
s2
(D) 2.8 N *s
(E) 0.0N* s
45. A Person stands on a scale in an elevator. She notices that the scale reading is lower than her
normal weight. Which of the following could possibly describe the motion of the elevator?
A)
B)
C)
D)
E)
It is moving down at a constant speed.
It is moving down and slowing down.
It is moving up and slowing down.
It is moving up and speeding up.
It is moving up with a constant speed.
FN = Fg
FN = Fg + Fnet
FN = Fg - Fnet
FN = Fg + Fnet
FN = Fg
A rock is thrown horizontally off a building form a height h, as shown. The
speed of the rock as it leaves the thrower’s hand at the edge of the building is vo.
46.
How much time does it take the rock to travel from the edge of the building to the ground?
(A)
h vo
(B)
h / vo
(C)
(D)
(E)
47.
h vo / g
2h/g
h = ho + voyt + ½ g t2
h = ½ g t2
since voy = 0 we can eliminate voyt
2h =t
g
2h/g
What is the kinetic energy of the rock just before it hits the ground?
(A)
1/2 (mgh)2
(B)
m vo2
(C)
½ mvox 2 – mgh
(D)
mgh
(E)
mgh + 1/2 mvox2
KEo + mgho = KE + mgh ( since h = 0 )
KEo + mgho = KE
½ mvox2 + mgho = KE
48.
Two people of unequal mass are initially standing still on ice with negligible friction. They then
simultaneously push each other horizontally. Afterward, which of the following is true?
(A) The kinetic energies of the two people are equal.(Does not have to be true )
(B) The velocity of the lighter person will be less than the heavier person (opposite is true)
(C) The momentum of the lighter person is greater than momentum of the heavier person ( must be
equal )
(D) The force that the lighter person puts on the heavier person is equal to the force the heavy person
puts on the first ( Conservation of Matter
(E) The less massive person has a smaller initial acceleration than the more massive person.
15 N
49.
12 N
2kg
FN = Fg + Fpush FN = 2*10m/s/s + 15 N = 35 N
Ffr = FN = .2 ( 35 N ) = 7 N
12 N – 7 N = 5 N
A block of mass 2 kg slides along a horizontal tabletop. A horizontal applied force of 12 N
and a vertical applied force of 15 N act on the block as shown above. If the coefficient of
kinetic friction between the block and the table is .2. the net force is approximately
A) 1 N
50.
B) 3 N
D) 5 N
E) 7 N
The driver of an automobile is initially traveling at constant velocity on a straight
road. Due to the sudden appearance of a pedestrian, the driver brakes and
decelerates with a magnitude of 15.0 m/s2 in order to avoid a collision. Which one
of the following statements concerning the automobile’s motion is correct?
(A)
(B)
(C)
(D)
(E)
51.
C) 4 N
The direction of the acceleration is in the same as the direction of the
displacement.
The direction of the acceleration is the same as the direction of the velocity.
The automobile travels a distance of 15.0 m only during the first second of
the deceleration.
The automobile travels a distance of 15.0 m during each second of the
deceleration.
The speed of the automobile decreases by 15.0 m/s during each second of the
deceleration. Definition of constant acceleration (deceleration )
During a space-walk, an astronaut of mass m pushes on a satellite of mass 2m with a
force F The force exerted by the satellite on the astronaut is
(A) 0
(B) -2F (C) 1/2 F (D) – F
(E) F
Newton’s 3rd Law Fastronaut on satellite + Fsatellite on astronaut = 0 Newton’s Third Law
speed m/s
speed as a function of time
12
10
8
6
4
2
0
Line 1
0
1
2
3
4
5
time in seconds
52.
The graph shows the speed of an object as a function of time. The average speed of
the object during the time interval shown is
Area = displament = ½ bh + bh + ½ bh = [ ½ 10 m/s ( 2s)] + [10 m/s (2s)] + [ ½ 10 m/s (1s) ] = 35m
v = displacement / time = 35 m / 5 s = 7 m/s
(A) 3 m/s
(B) 5 m/s
(C) 7 m/s (D) 8 m/s
(E) 10 m/s
53.
What is the total distance traveled by the object in the 5 seconds?
See above – in this case displacement = distance ( this is not always true )
(A) 2.5 m
(B) 5.0 m
(C) 7.5 m (D) 35 m (E) 37.5 m
Question 54 and 55
v
v
v
v
v
t
t
t
t
t
(A)
(B)
(C)
(D)
constant acceleration constant velocity decreasing velocity non constant acc
(E)
non constant acc
54. Which graph best describes the motion of a mass pulled by a constant net force?
(A)
(B)
(C)
(D)
(E)
55. Which graph best describes the motion of a mass pulled by a force that is equal to the
frictional acting on it is?
(A)
(B)
(C)
(D)
(E)
constant velocity
Question 56. A mass m splits
m
Before
2/3 m
1/3 m
After
-v
56. The velocity of the 1/3 part after the split is
(A) 1/3 v
po = p= 0
57.
(B) v
(C) 2/3 v
(D) 2 v
0 = 2/3 m ( - v) + 1/3 m ( ? v ) ? v = 2 v
(E) 3 v
A 70 kg person runs with a horizontal velocity of v and jumps into a 10 kg raft
floating just off shore. Assuming no water resistance, what will be the velocity
of the raft and person?
(A) 1/7 v
(B) 7 v
(C) 8/7 v
po = p= 70 kg ( v ) = (70kg + 10kg )voverall
(D) 7/8 v (E0
70kg v
= vorverall
(70kg + 10kg)
1/8 v
7/8 v = voverall
Question 58
The diagram below shows a 10 newton force pulling an 5.0 kg object up a hill at a constant
rate of 4 m / s. The hill is an elevation change of 2 m. Friction should be assumed to be
negligible.
B
W = F d = mg h = 5kg (10m/s/s) ( 2 m) = 100 J
10 N
2m
4 m/s
3m
58. How much work is done in moving the object from Point A to Point B
(A) 100 J
(B) 120 J
(C) 200 J
(D) 300 J
(D) 1200 J
59 An open railroad car filled with coal is coasting frictionlessly. A girl on board starts
throwing the coal horizontally backward straight off the car, one chunk at a time.
The car ( mrc + mcoal ) v = mcoal (-v) + mrc (+v) If mcoal is negative than mrc must be (+)
(A) speeds up (B) slows down
(C) first speeds up and then slows down
(D) travels at constant speed
(E) none of the above
60.
A .1 kg ball traveling 20 m/s is caught by a catcher. In bringing the ball to rest, the
mitt recoils for .01 seconds. The absolute value of the average force applied by the
glove is
(A) 20 N
(B) 100 N
(C) 200 N
(D) 1,000 N
nd
Newtons 2 law F =  mv
F = (.1kg ) ( 0 m/s – 20 m/s ) = 200 N
t
(.01s)
61. A rock is dropped off a cliff and strikes the ground with an impact velocity of 30 m/s.
How high was the cliff? v = vo + at vo = 0 m/s v / a = t
30 m/s / 10 m/s/s = 3.0s
(A) 15 m
(B) 20 m
(C) 30 m
(D)45 m (E) 60 m
y = yo + voyt + ½ gt2 voyt = 0 m/s y = ½ gt2 = ½ (10 m/s/s) ( 3.0s)2 = 45m/s
62.
A person who weighs 800 N steps onto a scale that is on the floor of an elevator car.
If the elevator accelerates upward at 5 m/s2, what will the scale read?
(A) 400 N
(B) 800 N
(C) 1000 N
(D) 1200 N
FN = Fg + Fnet = FN = 800 N + 80 kg ( 5 m/s2)
(E) 1600
63.
A force of 200 N is required to keep an object sliding at a constant speed of 2 m/s
across a rough floor. How much power is being expended to maintain this motion?
(A) 25 W
64.
(B) 50 W
(C) 100 W (D) 200 W (E) 400 W
Power = Force velocity = 200 N 2 m/s = 400 W
A ball of mass 0.5 kg initially at rest requires a speed of 4 m/s immediately after being
kicked by a force of strength 20 N. For how long did this force act on the ball? Newtons
2nd law F =  mv
t = mv = (.5kg) ( 4.0m/s – 0 m/s ) = .1s
t
F
20 N
(A) 0.01 s
(B) 0.02 s
(C) 0.1 s
(D) 0.2 s
(E) 1 s
65.
A box with a mass of 2 kg accelerates in a straight line from 4 m/s to 8 m/s due the
application of a force whose duration is 0.5 s. Find the average
strength of this force
(A) 2 N
(B) 4 N
(C) 8 N
(D) 12 N
nd
Newtons 2 law F =  mv
F = (2kg ) ( 8 m/s – 4 m/s ) = 16 N
t
(.5s)
(E) 16 N
66. A car slows down on a highway Its engine is providing a forward force of 1000 N. The
force of friction is 3000 N. It takes 20 s for the car to come to rest. What is the cars change in
momentum during these 20s?
a)
b)
c)
d)
e)
10,000kg m/s
20,000kg m/s
30,000kg m/s
40,000kg m/s
60,000kg m/s
Newtons 2nd law F =  mv
F t =  p = (-3000 N + 1000N) ( 20s )=p
t
 p = -40, 000 N s = -40,000 kg m/s
67. What mass is needed to put the following in rotational equilibrium?
0m
2m
2kg
4kg
4m
7m
6kg
A) 2 kg at 3m B) 2 kg at 5 m C) 0 kg D) 1 kg at 2 m
E) 1 kg at 6 m
2kg ( 10 m/s/s)(4m) + 4kg ( 10 m/s/s) (2m) + x ( 10m/s/s) x = 6kg (10m/s/s)(3m)
67. A thorium nucleus emits an alpha particle. Which of the following fundamental physics
principles can be used to explain why the direction of the daughter nucleus’s recoil must be in
the opposite direction of the alpha emission?
230
Ra
88
234
Th
90
4
He
2
I. Newton’s third law
II. Conservation of Momentum
po = p = 0 = mRa (-v) + ma(+v)
A) II only B) III only C) I and II only D) II and III only
III. Conservation of Energy
E) I, II, and III
68. A ball attached to a string is whirled around in a horizontal circle having a radius r. If the
radius of the circle is changed to 4r and the same centripetal force is applied by the string,
the new speed of the ball is which of the following?
(A)
(B)
(C)
(D)
(E)
One-quarter the original speed
One-half the original speed
The same as the original speed
Twice the original speed
Four times the original speed
Fc = mv2 = m ( ?v)2
R
4R
?v=2
69.
A racing car is moving around the circular track of radius 300 meters shown below. At the
instant when the car's velocity is directed due west, its acceleration is directed due south and has
a magnitude of 3 meters per second squared. When viewed from above, the car is moving
(A) clockwise at 30 m/s
(B) clockwise at 10 m/s
Acceleration = South ac = v2 rac = v2 (300m(3m/s2).5 =30
(C) counterclockwise at 30 m/s
r
m/s
(D) counterclockwise at 10 m/s
(E) with constant velocity
70. From the top of a high cliff, a ball is thrown horizontally with initial speed v0. Which of the
following graphs best represents the ball's kinetic energy K as a function of time t?
K = KEo + ½ mvoy2 Since voy is increasing than K will increase exponentially