PHYSICS 221
Summer 2007
EXAM 2: July 9 2007 9:50am—10:50am
Name (printed): ______________________________________________
Recitation Instructor: _________________________
Section #_______
INSTRUCTIONS:
This exam contains 12 equally weighted multiple-choice questions, numbered 51 through
62. 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, 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 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 electronic devices that are not permitted: Any laptop, palmtop, pocket
computer, PDA or e-book reader.
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. (01, 02, 03)
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 booklet. 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 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, Paula Herrera.
51. A particle of mass m = 1.5 kg is released from rest from the rim of a spherical
surface of radius R = 2.0 m . The particle slides down and up along the opposite
side, and comes momentarily to a stop at angle of 60° with the vertical (see
figure). What is the work done by friction?
a.
b.
c.
d.
e.
–15 J
–25 J
–30 J
–44 J
–52 J
m
60°
R
52. A 400-g box is pressed against a horizontal spring with constant k = 200 N/m.
When the spring is 5.0 cm shorter than its relaxed length, the box is released
(from rest). The box slides along a horizontal surface and into a 30° incline as
shown in the figure. Friction is negligible. What is the kinetic energy of the
particle when its height above the initial level is 20 cm?
θ = 30°
a.
b.
c.
d.
e.
0.25 J
0.53 J
0.62 J
0.78 J
The box never reaches that height.
53. The diagram below shows a potential energy U as a function of position x. Points
A and B are such that UA = UB.
U
A
B
x
Which of the following is true?
a.
b.
c.
d.
e.
The x component of the force is positive at both points.
The magnitude of the force at A and B is the same.
The work done by the force on a particle that moves from A to B is zero.
The particle oscillates between A and B.
None of the above.
54. A massive ten-wheeler truck and a light sport car moving at similar speeds toward
each other collide in a spectacular accident. Compare the change in momentum
and the change in velocity of each object due to the collision.
a.
b.
c.
d.
e.
Δpcar =
Δpcar <
Δpcar =
Δpcar >
Δpcar <
Δptruck ;
Δptruck ;
Δptruck ;
Δptruck ;
Δptruck ;
Δvcar =
Δvcar =
Δvcar >
Δvcar >
Δvcar <
Δvtruck
Δvtruck
Δvtruck
Δvtruck
Δvtruck
55. A 150-g ball that was traveling at 80 m/s at an angle of 30° below the horizontal
is hit by a racquet. The ball comes out vertically up, at 40 m/s. What is the
magnitude of the impulse exerted by the racquet on the ball?
a.
b.
c.
d.
e.
6.0 Ns
9.0 Ns
12 Ns
16 Ns
18 Ns
56. Two blocks with masses m1 and m2 = 3m1 move along a horizontal frictionless
G
G
surface with velocities v1 = 2v0 i and v2 = v0 j . They collide and stick to each
other. What is the final velocity of the combined body?
a. v0 ( 2i + 3 j )
b. v0 ( i − 3 j )
⎛ 3 ⎞
c. v0 ⎜ i + j ⎟
2 ⎠
⎝
3 ⎞
⎛
d. v0 ⎜ 2i + j ⎟
4 ⎠
⎝
⎛ i 3 ⎞
e. v0 ⎜ + j ⎟
⎝2 4 ⎠
57. A 2.0-kg block (A) slides on a frictionless surface at 3.0 m/s and hits a 4.0-kg
block (B) that was initially at rest. After the collision, block A is at rest and block
B moves into a spring with constant k = 100 N/m.
B
A
How much is the spring compressed?
a.
b.
c.
d.
e.
30 cm
37 cm
60 cm
73 cm
80 cm
58. A block of mass m is attached at the end of a massless, ideal string that is coiled
around a cylinder of mass M and radius R. When the system is released, the block
moves down and the cylinder rotates without friction on its axle. The string does
not slip on the cylinder. What is the magnitude and direction of the net torque on
the cylinder?
a.
b.
c.
d.
e.
τ < mgR, into the page
τ = mgR, into the page
τ < mgR, out of the page
τ = mgR, out of the page
None of the above.
M, R
m
The situation below refers to the next two questions:
A uniform cylinder of mass 2.0 kg and radius 50 cm is pulled by a horizontal string
through its center that applies a constant tension (see figure). The cylinder rolls
without slipping on a horizontal surface. After the cylinder has moved 3.0 m along
the surface, the speed of the center of mass is 4.0 m/s.
T
59. What is the magnitude of the tension in the string?
a.
b.
c.
d.
e.
5.3 N
8.0 N
11 N
14 N
20 N
60. What is the angular momentum of the cylinder at the end of the trajectory?
a.
b.
c.
d.
e.
2.0 kg m2/s
4.0 kg m2/s
8.0 kg m2/s
12 kg m2/s
24 kg m2/s
y
The situation below refers to the next two questions:
The two-dimensional object shown to the right is made
of eight identical uniform squares of side 1.0 m.
x
61. Determine the x component of the position of the center of mass.
a.
b.
c.
d.
e.
1.0 m
1.2 m
1.4 m
1.5 m
1.7 m
62. Now consider the following axes of rotation:
1: the y axis
2: the x axis
3: a line parallel to the x axis, at y = 1.5 m
Compare the moments of inertia for rotations about these axes.
a.
b.
c.
d.
e.
I1 < I3 < I2
I3 < I1 < I2
I3 < I2 < I1
I2 < I3 < I1
I2 < I1 < I3
Here you can write down your answers and keep this page to compare with the posted
solutions.
51
52
53
54
55
56
57
58
59
60
61
62