Physics 221 2007S
Exam 1
PHYSICS 221
Spring 2007
EXAM 1: Feb 15 2007 8:00pm—10:00pm
Name (printed): ____________________________________________
ID Number: ______________________________________________
Section Number: __________________________________________
INSTRUCTIONS:
Each question is of equal weight, answer all questions. All questions are multiple choice.
Choose the best answer to each question.
Before turning over this page, put away all materials except for pens, pencils, erasers,
rulers, your calculator and “aid sheet”. An “aid sheet” is one two sided 8½×11 page of
notes prepared by the student. There is also a list of possibly useful equations at the end
of the exam.
"In general, any calculator, including calculators that perform graphing numerical
analysis functions, is permitted. Electronic devices that can store large amounts of text,
data or equations are NOT permitted." If you are unsure whether or not your calculator
is allowed for the exam ask your TA.
Examples of allowed calculators: Texas Instruments TI-30XII/83/83+/89, 92+
Casio FX115/250HCS/260/7400G/FX7400GPlus/FX9750 Sharp EL9900C.
Examples of electronic devices that are not permitted: Any laptop, palmtop, pocket
computer, PDA or e-book reader.
In marking the multiple choice bubble sheet use a number 2 pencil. Do NOT use ink. If
you did not bring a pencil, ask for one. Fill in your last name, middle initial, and first
name. Your ID is the middle 9 digits on your ISU card. Special codes K to L are your
recitation section, for the Honors section please encode your section number as follows:
H1⇒02; H2⇒13 and H3⇒25.
If you need to change any entry, you must completely erase your previous entry. Also,
circle your answers on this exam. Before handing in your exam, be sure that your
answers on your bubble sheet are what you intend them to be.
It is strongly suggested that you circle your choices on the question sheet. You
may also copy down your answers on a piece of paper to take with you and compare
with the posted answers. You may use the table at the end of the exam for this.
When you are finished with the exam, place all exam materials, including the bubble
sheet, and the exam itself, in your folder and return the folder to your recitation
instructor. No cell phone calls allowed. Either turn off your cell phone or leave it at home.
Anyone answering a cell phone must hand in their work; their exam is over.
Total number of questions is 27. Question 27 is “extra credit”
Best of luck, David Atwood and Paula Herrera-Siklody
Page 1 of 17
Physics 221 2007S
Exam 1
[1] If a 200kg box is subject to a net force of magnitude 100N, what is the magnitude of
its acceleration?
(A) 0.25 m/s 2
(B) 0.50 m/s 2
(C) 1.0 m/s 2
(D) 2.0 m/s 2
(E) 4.0 m/s 2
[2] A car is traveling in a circular track at a constant speed of 20m/s. If the magnitude of
the acceleration of the car is1 m/s 2 , what is the radius of the track?
(A) 50m
(B) 100m
(C) 200m
(D) 400m
Page 2 of 17
(E) 800m
Physics 221 2007S
Exam 1
[3] An elevator has a mass of 600kg, not including passengers. The elevator is designed
to ascend, at a constant speed, a vertical distance of 20.0m (i.e. five floors) in 16.0s, and
is driven by a motor that can provide up to 30kW of power. What is the maximum
number of passengers that can ride in the elevator? Assume that an average passenger has
a mass of 65kg.
(A) 28
(B) 24
(C) 20
(D) 16
(E) 12
[4] A person pulls a 20-kg block up a ramp of height h = 10 m and angle θ = 20° at
constant speed. The rope makes an angle φ = 35° with the ramp as shown and has a
tension of 160N . Find the work done by kinetic friction.
(A) −661J
(D) −1880J
(B) −740J
(E) −5800J
(C) −980J
Page 3 of 17
Physics 221 2007S
Exam 1
[5] A bullet of mass 1g is fired at a block of wood traveling at a speed of 300 m/s. It
comes to rest 60μs after hitting the surface of the wood. If you assume that the wood
slows down the bullet exerting a constant force against the bullet’s motion, what is the
magnitude of that force?
(A) 2500N
(B) 5000N
(C) 7500N
(D) 10000N
(E) 25000N
[6]A lady bug and a gentleman bug are sitting on a circular turntable with radius 50cm
which is rotating clockwise at a constant angular velocity. The ladybug is at the rim of
the turntable while the gentleman bug is half way between the center and the rim. If the
lady bug is moving at a speed of 0.10m/s, what is the magnitude of the angular velocity
of the gentleman bug?
(A) 0.05 rad/s
(B) 0.10 rad/s
(C) 0.20 rad/s
Page 4 of 17
(D) 0.30 rad/s
(E) 0.40 rad/s
Physics 221 2007S
Exam 1
[7]Sally runs 1 km north at 6 m/s and then runs 2 km south at 4 m/s. What is the
magnitude of Sally’s average velocity for this trip?
(A) 0.0 m/s
(B) 1.5 m/s
(C) 2.0 m/s
(D) 3.0 m/s
(E) 5.0 m/s
[8]An object's height as a function of time is y (t ) = (120 m) + (80 m/s)t − (20 m/s 2 )t 2 .
What is the highest point this object reaches?
(A) 100m
(B) 150m
(E) None of the above
(C) 300m
Page 5 of 17
(D) 400m
Physics 221 2007S
Exam 1
[9]A 100kg person stands on top of a box that is inside the cabin of an elevator. The
elevator has an upward acceleration of 3 m/s 2 . What is the magnitude of the net force
acting on the person?
(A) 100N
(B) 300N
(C) 680N
(D) 980N
(E) 1280N
[10]The figure shows the overhead view of two stones that travel in circles over a
frictionless horizontal surface. Each stone is tied to a cord whose opposite end is
anchored at the center of the circle. The radius of the circle of stone B is 2 times the
radius of the circle of stone A. The tension in the long cord is 2 times the tension in the
short cord. The period of stone B is 4 times the period of stone A. What is the ratio
(mass of stone B):(mass of stone A)
(A) 16:1
(D) 1:4
(B) 4:1
(E) 1:16
(C) 1:1
A
Page 6 of 17
B
Physics 221 2007S
Exam 1
[11] A rubber ball is tossed horizontally from a window 5m above a parking lot. When it
strikes the ground it rebounds. Which of the following graphs best represents the ycomponent of the ball’s velocity as a function of time? The +y direction is up and neglect
air resistance.
vy A
vy
vy
B
C
Time
Time
vy
vy
D
Time
E
Time
Page 7 of 17
Time
Physics 221 2007S
Exam 1
[12] Robin Hood fires an arrow at velocity v0=30m/s at an angle of θ=30o above the
horizontal from the top of a cliff of height 20m. The sheriff of Nottingham stands at
distance d from the base of the cliff. What is the speed of the arrow when it strikes the
sheriff? Neglect air resistance.
(B) v=42 m/s
(C) v=46 m/s
(A) v=36 m/s
(E) Cannot determine the speed without knowing d.
Robin
Hood
v0=30m/s
(D) v=50 m/s
θ=30o
h20m
v=?
d
Page 8 of 17
Sheriff of
Nottingham
Physics 221 2007S
Exam 1
G
G
G
[13] Vectors A and B start at a corner of a cube of edge length 1. Vector A lies along
G
the edge of the cube. Vector B goes to the opposite corner of the cube. What is the angle
G
G
between A and B ?
(A) 45°
(B) 55°
(C) 60°
(D) 70°
(E) 90°
1
[14] A particle of mass m = 10.0 kg moves along the x-axis with time dependent
acceleration ax = ( 3.00 m/s 4 ) t 2 . The velocity of the particle at t = 0 is -3.00 m/s in the +x
direction. What is the velocity of the particle at t = 2.00s?
(A) 0 m/s
(B) 5 m/s
(C) 8 m/s
(D) 9 m/s
Page 9 of 17
(E) 21 m/s
Physics 221 2007S
Exam 1
[15] Two cars move along parallel tracks on a straight road. Shown below are the
snapshots taken every second. Assume that the motion between snapshots is what one
would assume from the image, nothing strange. Which of the following best describe the
direction of the velocity of the rectangular car relative to the square car at t = 2 s and at t
= 3 s?
(A) ← , →
1s
(B) ← , ←
2s
1s
(C) → , →
3s
2s
3s
(D) ← , 0
4s
4s
Page 10 of 17
(E) → , 0
Physics 221 2007S
Exam 1
The following information applies to questions [16] and [17]: In the figures below,
the force applied in both cases on the system has the same magnitude and is horizontal.
Block A has twice the mass of block B. There is no friction between the blocks and the
surface underneath them.
F
mA
mA
mB
mB
Figure 2
Figure 1
[16] What is the magnitude of the net force on block A in figure 1 and figure 2,
respectively?
(A) F ,
2F
,
3
F
(C)
,
3
2F
(D)
,
3
F
(E)
,
3
(B)
F
3
F
3
2F
3
2F
3
F
3
[17] For the same figures in the previous problem, which of the following is TRUE?
(please read carefully)
(A) The force on A by B is smaller in figure 1 than in figure 2.
(B) The force on A by B is the same in both figures.
(C) In figure 1, the force on A by B is smaller than the force on B by A.
(D) In figure 2, the force on A by B is smaller than the force on B by A.
(E) None of the above.
Page 11 of 17
F
Physics 221 2007S
Exam 1
[18]A block of mass 2kg moving along the x-axis is subject to a position dependent force
given by
G
F = Ax 2 iˆ
where A = 2 kg/(ms 2 ) . Initially the block is at x=0m and has a velocity of (10 m/s) iˆ .
When the block reaches x=4m, what is its kinetic energy?
(A) 43J
(B) 57J
(C) 100J
(D) 143J
(E) 228J
[19] A 10-kg weight hangs from two ideal massless ropes as shown below. Find the
tension on the left rope.
(A) 33 N
(B) 49 N
(C) 85 N
(D) 98 N
(E) 113 N
30°
60°
T=?
10kg
Page 12 of 17
Physics 221 2007S
Exam 1
[20] City B is 1000km east of city A. A light plane can fly at a speed of 400km/hr with
respect to the air. If there is a constant wind at a speed of 300km/hr blowing in a direction
30° north of east, what is the time it takes for the plane to make the trip from A to B?
(A) 2.65 hr
(B) 2.20 hr
(E) The trip as described is not possible.
(C) 1.59 hr
(D) 1.46 hr
[21] For the vectors shown below, which of the following statements is TRUE?
G G G G
(A) A ⋅ C = A ⋅ D
G G G G
(B) A ⋅ B > A ⋅ C
G G G G
(C) C ⋅ B = C ⋅ D
G G
G G
(D) A ⋅ B = − A ⋅ D
G G
G G
(E) B ⋅ C = −C ⋅ B
A
D
B
C
Page 13 of 17
Physics 221 2007S
Exam 1
[22]A block of mass 10kg lies at rest on an incline ramp tilted at an angle of 10º to the
horizontal. The coefficient of static friction between the block and the ramp is μS=0.4.
The coefficient of kinetic friction between the block and the ramp is μK=0.3. What is the
magnitude of the frictional force on the block?
(A) 0N
(B) 17N
(C) 29N
(D) 39N
(E) 49N
[23] A 2kg cannon ball is fired from ground level at an angle of 45° with respect to the
horizontal. The ball hits a castle on a cliff which is 600m away horizontally and 200m
above the ground. What was the initial speed of the cannon ball? Neglect air resistance.
(A) 43 m/s
(B) 63 m/s
(C) 66 m/s
Page 14 of 17
(D) 94 m/s
(E) 112 m/s
Physics 221 2007S
Exam 1
G
G G
G G
G
[24] Let A and B be two vectors such that A + B = 2 and A − B = 4 . What is the value
G G
of A · B ?
(A) 0
(C) −1
(B) −1/ 2
(D) −2
(E) −3
[25] Consider the system shown below made of three identical blocks of mass m, two
ideal, massless strings and an ideal, massless pulley. The friction between the blocks and
the table is negligible. A force of F=mg is applied to the end of the string as shown.
m
T1
m
T2
m
F=mg
Let T1 and T2 be the tension on each string, as shown in the figure. Which of the
following is true?
(A) T1 = T2 = mg
(B) 2T1 = T2 = mg
(C)2T1 = T2 = 23 mg
(D)T1 = T2 = 23 mg
(E)T1 = T2 = 32 mg
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Physics 221 2007S
Exam 1
[26] Ball A is dropped from the top of a building of height h at the same instant that ball
B is thrown vertically upward from the ground. When the balls collide, they are moving
in opposite directions, and the speed of A is two times the speed of B. How far above the
ground does the collision occur?
(A) h/6
(B) h/3
(C) h/2
(D) 2h/3
(E) 5h/6
[27] [EXTRA CREDIT PROBLEM] A crate is dragged at constant speed along a
horizontal floor with a cable at an angle with the horizontal (see figure). Let these
symbols represent the magnitude of the following forces on the crate:
T = tension in the cable
f = friction force
N = normal force by the floor
W = weight of the crate
T
Which of the following is TRUE?
(A)
(B)
(C)
(D)
(E)
T>f
T<f
T<f
T>f
T>f
;
;
;
;
;
N<W
N=W
N<W
N=W
N>W
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Physics 221 2007S
Exam 1
You may record your answers on this page and take it with you after the exam to
compare to the posted solutions. Solutions posted: On WebCT about 1 hour after exam;
Grades posted: Friday afternoon after the exam.
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