PHYSICS 221
Fall 2007
EXAM 1: October 3, 2007 8:00pm—10:00pm
Name (printed): ______________________________________________
Recitation Instructor: _________________________
Section #_______
INSTRUCTIONS:
This exam contains 25 multiple-choice questions plus 2 extra credit questions, each worth 3
points. Choose one answer only for each question. Choose the best answer to each question.
Answer all questions.
Allowed material: Before turning over this page, put away all materials except for pens, pencils,
erasers, rulers and your calculator. There is a formula sheet attached at the end of the exam.
Other copies of the formula sheet are not allowed.
Calculator: In general, any calculator, including calculators that perform graphing, is permitted.
Electronic devices that can store large amounts of text, data or equations (like laptops, palmtops,
pocket computers, PDA or e-book readers) are NOT permitted. If you are unsure whether or not
your calculator is allowed for the exam, ask your TA.
How to fill in the bubble sheet:
Use a number 2 pencil. Do NOT use ink. If you did not bring a pencil, ask for one.
Write and fill in the bubbles corresponding to:
- Your last name, middle initial, and first name.
-   Your ID number (the middle 9 digits on your ISU card)  
- Special codes K to L are your recitation section. (Honors section, please enter 24).
Always use two digits (e.g. 01, 09, 11, 13)
Please turn over your bubble sheet when you are not writing on it.
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. 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.
Best of luck, Paul Canfield and Paula Herrera
Physics 221 Fall 2007 Exam 1
1. A book is at rest on a desk top. Which of the following forces forms a Newton’s third
law pair with the book’s weight?
A) The normal force of the table on the book
B) The force of the book on the table
C) The gravitational force of the earth on the book
D) The gravitational force of the book on the earth
E) None of the above
2. A 65 kg student is standing in a high speed elevator as it accelerates upward with
a = 15 m/s2. What is the magnitude of the normal force that the floor of the elevator
exerts on the student?
A) 338 N
B) 637 N
C) 975 N
D) 1274 N
E) 1612 N
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Physics 221 Fall 2007 Exam 1
3. Three blocks are arranged on a horizontal, frictionless table as shown below. If a
force of 20.0 N to the right is applied to the left mass, what is the horizontal force on
the far right mass?
A) 0.606 N
B) 1.82 N
C) 7.93 N
D) 12.2 N
E) None of the above
20.0 N
20.0 kg
10.0 kg
3.0 kg
4. The speed 150 feet / hour (ft/h) converted into S.I. units is:
A) 4.16 × 10–2 ft/s
B) 5.00 × 10–1 in/s
C) 45.7 m/h
D) 1.27 ×10–2 m/s
E) 0.762 m/min
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Physics 221 Fall 2007 Exam 1
5. An object’s acceleration is shown below. The object starts at rest at x = 0 and t = 0.
What is the object’s position at time t = 3.0 s?
A) 4.5 m
B) 9.0 m
C) 12.5 m
D) 15 m
E) 25 m
ax (m/s2)
5.0
5.0
t (s)
6. How long does the mass, initially at rest at the top of the incline, take to slide down
the frictionless, inclined plane shown below?
35.0°
5.00 m
A) 0.84 s
B) 1.01 s
C) 1.11 s
D) 1.33 s
E) 1.47 s
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Physics 221 Fall 2007 Exam 1
7. Two balls are shot toward each other at the same time, t = 0 s, off of two identical
tables that are 100 m apart. Let ball #1 hit the ground at t1 and ball #2 hit the ground
at t2. If the initial velocity of ball #1 is ( 2.0 m/s ) iˆ and the initial velocity of ball #2 is
( −4.0 m/s ) iˆ , what is the ratio of t1:t2?
Ignore friction and air resistance or drag.
A) 4 : 1
B) 2 : 1
C) 1 : 1
D) 1 : 2
E) 1 : 4
8. A flatbed truck is carrying a 50.0 kg box. Both the truck and box are at rest at a stop
light. When the light turns green, what is the maximum acceleration that the truck
can have that avoids having the box slip if µS = 0.300 and µK = 0.150?
a
m
A) 0.98 m/s2
B) 1.47 m/s2
C) 1.96 m/s2
D) 2.94 m/s2
E) 4.90 m/s2
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Physics 221 Fall 2007 Exam 1
9. A particle moves along the path shown below with constant speed, passing point A
first and point E last. At which point does the particle have an acceleration that points
to the right?
10. A mass is tied to string and undergoes uniform circular motion on a frictionless,
horizontal table. The string will break if its tension exceeds 100 N. Which of the
following statements is true if the mass is 10 kg and the period of the motion is 1.0 s?
A) The radius of the circle has to be less than 0.25 m.
B) The radius of the circle has to be greater than 0.25 m.
C) The radius of the circle has to be less than 0.50 m.
D) The radius of the circle has to be greater than 0.50 m.
E) Since the mass is moving with a constant speed, the radius of the circle can be
any size.
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Physics 221 Fall 2007 Exam 1
11. A worker is lowering a 100 kg mass with a downward acceleration of 2.0 m/s2 as
shown below. What is the tension in the massless rope at the point indicated by the
asterisk (*)?
A) 1180 N
B) 980 N
C) 780 N
D) 490 N
E) 390 N
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Physics 221 Fall 2007 Exam 1
12. A river of width 200 m runs from the north to the south with a current of 2.0 m/s. If
you can swim with a speed of 4.0 m/s (with respect to the water), what angle from the
east should you point if you want to swim directly across the river?
A) 27º
B) 30º
C) 45º
D) 60º
E) This is not possible for any angle.
θ?
current
200 m
13. A particle, moving with constant acceleration, covers the distance between two points
that are 200 m apart in 5.0 s. If its speed at the second point is 50 m / s, what was its
speed at the first point?
A) 20 m/s
B) 30 m/s
C) 40 m/s
D) 50 m/s
E) 80 m/s
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Physics 221 Fall 2007 Exam 1
14. The sketch below shows the x-dependence of a force. Which point (or points) is a
stable equilibrium point(s)?
A) A
B) B
C) C
D) D
E) both B and D are stable equilibrium points.
G
15. What is the angle between vector A = 3iˆ + 4 ˆj − 2kˆ and the x axis?
A)
B)
C)
D)
E)
37°
53°
56°
61°
65°
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Physics 221 Fall 2007 Exam 1
16. A particle undergoes uniform circular motion. The magnitude of its velocity is 5.0
m/s and the magnitude of its radial acceleration is 10 m/s2. What is the radius of the
circle?
A)
B)
C)
D)
E)
0.4 m
0.5 m
2.0 m
2.5 m
2.8 m
17. Water comes out of a garden hose at 10 m/s. The hose, whose end is horizontal and
1.5 m above the ground, is aimed at a vertical wall located 2.0 m away. At what
distance from the base of the wall does the water hit the wall?
water
1.5 m
?
2.0 m
A)
B)
C)
D)
E)
0.2 m
0.4 m
0.7 m
1.1 m
1.3 m
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Physics 221 Fall 2007 Exam 1
18. A 1.0 kg box is placed on a 20-m high point on a hill and released from rest. When
the box reaches the bottom of the slope, its speed is 10 m/s. Determine the work done
by friction.
A) –50 J
B) –96 J
C) –146 J
D) –196 J
E) It cannot be determined
because µk is not given.
20 m
19. A ball tossed vertically into the air takes 2.0 s to come back to the original position.
How high does the ball go (above its initial position)? Ignore friction and drag.
A)
B)
C)
D)
E)
4.9 m
9.8 m
15 m
20 m
25 m
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Physics 221 Fall 2007 Exam 1
20. A pendulum made of a light string and a small bob is released from the position
where the string makes an angle of 30° with respect to the vertical. Right at the
bottom of the bob’s trajectory, the string snaps. Which of the following diagrams
correctly depicts the velocity of the bob and the forces acting on it right after the
string snaps?
30°
v
v
T
v
mg
mg
A
mg
B
C
v
T
v
mg
mg
D
E
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Physics 221 Fall 2007 Exam 1
21. A 2.0 kg block slides at constant speed down an incline that makes an angle of 30°
with the horizontal. What is the coefficient of kinetic friction between the block and
the incline?
A)
B)
C)
D)
E)
0.22
0.50
0.58
0.87
0, because the speed is constant.
22. A turntable rotates at 30 rpm (revolutions per minute) at t = 0. Due to friction with the
surface underneath it, it slows down and stops in 4.0 s. How many turns did it
complete in this time?
A)
B)
C)
D)
E)
1.0 turns
1.3 turns
2.0 turns
2.2 turns
3.1 turns
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Physics 221 Fall 2007 Exam 1
23. The graph below shows the potential energy of a force as a function of x.
Potential energy
1 square = 1 J × 1 m
x
Rank the x component of the force (including signs!) associated with this potential at
points x = –2 m, x = –1 m and x = 5 m
A)
B)
C)
D)
E)
Fx(–1 m) < Fx(–2 m) = Fx(5 m)
Fx(–1 m) < Fx(–2 m) < Fx(5 m)
Fx(–1 m) < Fx(5 m) < Fx(–2 m)
Fx(5 m) < Fx(–2 m) < Fx(–1 m)
None of the above.
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Physics 221 Fall 2007 Exam 1
24. A 10-kg block is pulled along a horizontal floor by a massless rope that makes an
angle of 35° above the horizontal. The tension in the rope is 100 N. What is the
magnitude of the normal force by the floor on the block?
A)
B)
C)
D)
E)
18 N
41 N
57 N
98 N
120 N
25. Two blocks of masses m and 3m are connected through a massless, ideal string that
goes through an ideal, massless pulley in the arrangement shown below. There is no
friction between the blocks and the surfaces. Determine the tension in the string.
A)
B)
C)
D)
E)
3
mg
2
mg
1
mg
2
1
mg
4
3
mg
8
m
3m
30°
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Physics 221 Fall 2007 Exam 1
26. A 1.0-kg block compresses a spring with k = 2000 N/m and is then released. The
block then slides along a frictionless track and into a circular loop of radius
R = 50 cm (see figure). At the top of the loop, the normal force on the block by the
track has a magnitude equal to twice the weight of the block. How much was the
spring compressed at the beginning?
A)
B)
C)
D)
E)
5.0 cm
10 cm
13 cm
28 cm
32 cm
R
k
m
27. A 200 g mass is attached to a spring (k = 30 N/m) that is compressed 10 cm from its
equilibrium position. If the coefficient of friction between the mass and the table is
µK = 0.50, what is the velocity of the mass when the spring has expanded by 5.0 cm
(i.e. when the spring is only compressed by 5.0 cm)?
k
µK
m
x = −10 cm x = −5.0 cm
x=0
A) 0.61 m/s
B) 0.80 m/s
C) 1.1 m/s
D) 1.2 m/s
E) None of the above
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Physics 221 Fall 2007 Exam 1
You may record your answers on this page and take it with you after the exam to
compare to the posted solutions.
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