TIME
OF
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DEPARTMENT OF NATURAL SCIENCES
PHYS 2211, Exam 3
Version 2
Total Weight: 100 points
Section 1
November 15, 2013
1.
Check your examination for completeness prior to starting. There are a total of nine (9)
problems on seven (7) pages.
2.
Authorized references include your calculator with calculator handbook, and the Reference
Data Pamphlet (provided by your instructor).
3.
You will have 50 minutes to complete the examination.
4.
The total weight of the examination is 100 points.
5.
There are five (5) multiple choice and four (4) calculation problems. Work all multiple choice
problems and 3 calculation problems. Show all work; partial credit will be given for correct work
shown.
6.
If you have any questions during the examination, see your instructor who will
be located in the classroom.
7.
Start:
Stop:
11:00 a.m.
11:50 a.m
PROBLEM
POINTS
1-6
25
7
25
8
25
9
25
TOTAL
100
PERCENTAGE
CREDIT
CIRCLE THE SINGLE BEST ANSWER FOR ALL MULTIPLE CHOICE QUESTIONS. IN
MULTIPLE CHOICE QUESTIONS WHICH REQUIRE A CALCULATION SHOW WORK FOR
PARTIAL CREDIT.
1. A dumbbell-shaped object is composed by two equal masses, m, connected by a rod of
negligible mass and length r. If I1 is the moment of inertia of this object with respect to an
axis passing through the center of the rod and perpendicular to it and I2 is the moment of
inertia with respect to an axis passing through one of the masses, it follows that
a.
I1> I2.
b.
I2 > I1.
c.
I1 = I2.
2. A very light rod with two identical masses attached to it is rotating in the
counterclockwise direction around the axis which goes through one of the rod’s ends (O)
as shown below. The direction of the angular velocity of the mass A is
a.
Out of the page.
b.
Into the page.
c.
To the left.
d.
To the right.
e.
Tangential to the mass’s trajectory.
(5)
3. A very light rod with two identical masses attached to it is rotating in the
counterclockwise direction around the axis which goes through one of the rod’s ends (O)
as shown above. The system speeds up as it rotates. Check all that apply.
a.
A and B have the same tangential acceleration.
b.
The angular velocity of B is twice as great as the angular velocity of A.
c.
B is moving twice as fast as A. In angular sense!
(5)
d.
The tangential acceleration of B is twice as great as the tangential acceleration of
A.
e.
The tangential acceleration of A is twice as great as the tangential acceleration of
B.
4. On which of the following does the moment of inertia of an object depend? Check all
that apply.
a.
Linear speed.
b.
Linear acceleration.
c.
Angular speed.
d.
Angular acceleration.
e.
Total mass.
f.
Shape and density of the object.
g.
Location of the axis of rotation.
(5)
5. For an INELASTIC collision, which of the following statements are true?
Choose all that apply.
a.
Momentum is gained.
b.
Kinetic energy is lost.
c.
Kinetic energy is conserved.
d.
Momentum is lost.
e.
Momentum is conserved.
f.
Kinetic energy is gained.
(5)
PHYS 2211 Exam 3, Version 2
Fall 2013
3
6. In a lab environment, you are investigating the impulse of a force exerted on a brick when the
brick's speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a
secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into
a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater
impulse of the force on the brick?
a.
There is a greater impulse of the force on the brick from the gelatin.
b.
There is a greater impulse of the force on the brick from the wall.
c.
Not enough information is given to determine the answer.
d.
The impulse is the same in both situations.
(5)
7. A 1.15-kg grinding wheel 22.0 cm in diameter is spinning counterclockwise at a rate of 20.0
revolutions per second. When the power to the grinder is turned off, the grinding wheel slows with
constant
angular acceleration and takes 80.0 s to come to a rest.
a. What was the angular acceleration (in rad/s2) of the grinding wheel as it came to rest if we
take a counterclockwise rotation as positive?
0  20.0 rev / s  125.7 rad / s

 0
 1.57 rad / s 2
t
b. How many revolutions did the wheel make during the time it was coming to rest?
 2  0 2  2 (   0 )
 0
 
 5028.8 rad  800 rev
2
2
c.What is the magnitude of the tangential acceleration of the point on the rim of the
PHYS 2211 Exam 3, Version 2
Fall 2013
4
wheel?
at  r  0.173 m / s 2
are at the controls of a particle accelerator, sending a beam of 4.20×107m/s protons
(mass 1.67262178 × 10-27 kilograms) at a gas target of an unknown element. Your detector tells
you that some protons bounce straight back after a collision with one of the nuclei of the
unknown element. All such protons rebound with a speed of 3.90×107 m/s. Assume that the
initial speed of the target nucleus is negligible and the collision is elastic.
8. You
a. Find the mass of one nucleus of the unknown element.
m1V1I  m1V1 f  m2V2 f
V1i  V1 f  V2 f
m2 
m1V1i  m1V1 f
V1i  V1 f
 27m1  4.52  10  26 kg
b. What is the speed of the unknown nucleus immediately after such a collision?
V1i  V1 f  V2 f
V2 f  0.300  10 7 m / s
9. A 3.00 kg stone is sliding to the right on a frictionless horizontal surface at 6.00 m/s when it is
suddenly struck by an object that exerts a large horizontal force on it for a short period of time.
The graph in the figure below shows the magnitude of this force as a function of time.
PHYS 2211 Exam 3, Version 2
Fall 2013
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a. What impulse does this force exert on the stone?
I=area under the F-vs-t curve
I  (1.00  10 3 s)(2.50  10 3 N )  2.50 Ns
(25)
b. Just after the force stops acting, find the magnitude of the stone's velocity if the force acts
to the right.
I  mV f  mVi
V f  I / m  Vi  6.83 m / s
c. Just after the force stops acting, find the direction of the stone's velocity if the force acts
to the right.
To the right (velocity is positive)
PHYS 2211 Exam 3, Version 2
Fall 2013
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