ame: ________________________ Class: ___________________ Date: __________
Exam 3--PHYS 201--F12--Ch 5-8
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. Which of the following is an example of a nonconservative force?
a. gravity
b. magnetism
c. friction
d. Both choices a and b are valid.
____
2. If both mass and velocity of a ball are tripled, the kinetic energy is increased by a factor of:
a.
b.
c.
d.
____
3. The unit of work, joule, is dimensionally the same as which of these?
a.
b.
c.
d.
____
newton/second.
newton/kilogram.
newton-second.
newton-meter.
4. Which of the following is that form of energy associated with an object's motion?
a.
b.
c.
d.
____
3.
6.
9.
27.
potential
thermal
bio-chemical
kinetic
5. In a system with two moving objects, when a collision occurs between the objects:
a. the total kinetic energy is always conserved.
b. the total momentum is always conserved.
c. the total kinetic energy and total momentum are always conserved.
d. neither the kinetic energy nor the momentum is conserved.
1
____
6. If the momentum of an object is tripled, its kinetic energy will change by what factor? (Assume the mass of
the object remains the same.)
a.
b.
c.
d.
____
7. A system of particles has a momentum of zero. Which of these statements is true about the kinetic energy of
the system?
a.
b.
c.
d.
____
the kinetic energy is zero
the kinetic energy is positive
the kinetic energy is negative
there is not enough information
8. A bouncy rubber ball and bean bag, each with the same mass, fall to the floor from the same height. Which
of these statements about the force imparted to the floor is true?
a.
b.
c.
d.
____
zero
one-third
three
nine
the rubber ball imparts a greater force
the bean bag imparts a greater force
the ball and bean bag impart the same force
there is not enough information
9. Kaisa sits on the outer rim of a merry-go-round, and Chad sits midway between the rim and center.
The merry-go-round makes 1 revolution every 2 seconds. Chad’s linear velocity is ...
a.
b.
c.
d.
e.
same as Kaisa’s
one-half of Kaisa’s
one-quarter of Kaisa’s
twice Kaisa’s
four times Kaisa’s
2
____ 10. A ball tied to a string is being whirled around in a circle. What can you say about the force of tension on the
ball?
a.
b.
c.
d.
the tension is tangent to the circular path
the tension acts towards the center of the circular path
the tension acts away from the center of the circular path
none of these
____ 11. A grindstone spinning at the rate of 8.3 rev/s has what angular speed in rad/s?
a.
b.
c.
d.
3.2 rad/s
26 rad/s
52 rad/s
81 rad/s
____ 12. An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle
θ in the time t, through what angle did it rotate in the time 1/2 t?
a.
b.
c.
d.
e.
1
θ
2
3
θ
4
1
θ
4
2θ
4θ
3
____ 13. This figure shows four identical L-shaped objects. Each rotates around the axis drawn with the thin black
line. Rank the four objects from greatest moment of inertia to the least moment of inertia.
a.
b.
c.
d.
c>d>b>a
d>c>b=a
c>d>a=b
a=b=c=d
____ 14. Which of these are the basic SI units for moment of inertia?
m2
s2
a.
kg
b.
m
c.
d.
kg m 2
m
kg
2
s
____ 15. Two spheres have the same mass. One sphere is made of aluminum, while the other sphere is made of gold.
Both are solid. Because gold is more dense, the radius of the gold sphere is smaller than the aluminum
sphere. Which has the larger moment of inertia?
a.
b.
aluminum sphere
gold sphere
c.
d.
4
both the same
not enough information
Problem
16. (25 pts) A uniform solid sphere that can rotate about its central point in any direction. The sphere
has a radius of 2 m and a mass of 30 kilograms and is initially at rest. Starting at time t=0, a force of
12i8 − 2k8 Newtons is applied at the point on the sphere with coordinates (2.0, 1.0, 0) meters.
a) What is the torque applied to the sphere?
b) After 3 seconds, what is the kinetic energy of the sphere?
-
5
17. (10 pts) A 4.0 kg mess kit sliding on a frictionless surface explodes in two different sized parts, one
has a mass of 3 kg and is moving with velocity −3i8 + 4j8 + 6k8 m/s, the other has a mass of 1kg and is
moving at 6i8 − 10j8 − 2k8 m/s. What is the original velocity (in vector notation) of the mess kit?
-
6
18. (20 pts) A bug, fitted with a metal collar, slides back and forth in a bowl 0.11 m deep,
starting from rest at the top, as shown in this figure. The bug has a mass of 0.010 kg.The
bowl is frictionless, but, at the bottom, a magnetic force acts on the bug over a 0.015 m
patch. This force is dependent on the position of the bug as defined by this function:
F = 2x
Assume the force acts symmetrically (that is, the same force is experienced regardless of
the bug’s direction).
a) What is the bug’s total energy at the top of the bowl?
b) How much energy does the bug lose when it crosses through the magnetic field?
c) What is the bug’s speed at the bottom on its first pass, just after it goes across the
magnetic patch?
d)How many times does the bug cross the 0.015 m patch?
-
7
A man has a moment of inertia of 100 kg m2. He stands on a rotating platform
(with negligible moment of inertia) and is initially at rest. The man has a 1.0 kg mass
attached to a rope of length 2.0 m. He swings the mass on a rope at a rate of 1.2 rev/s
in the clockwise direction. What is the magnitude and direction of the man’s angular
speed when he swings the mass?
19. (15 pts)
.
8
ID: A
Exam 3--PHYS 201--F12--Ch 5-8
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
C
D
D
D
B
D
D
A
B
B
C
C
C
C
A
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
DIF: 1
PROBLEM
16. ANS:
PTS: 1
17. ANS:
PTS: 1
18. ANS:
PTS: 1
19. ANS:
.
PTS: 1
1