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Quiz 4--PHYS 101-3T--F13
Multiple Choice
Identify the choice that best completes the statement or answers the question.
5. A boy swings a 2.0 kg stone in a horizontal
1. Consider a child who is swinging. As she reaches
the lowest point in her swing
a. the tension is equal to the centripetal force
b. the tension is less than the weight
c. the tension is greater than the weight
d. the tension equals mass*acceleration
circle with a radius of 2.0 m. The
string breaks when the stone rotates at 2
rad/s. What tension in the string will cause
it to break?
2. A rigid object is rotating with an angular speed ω<
0. The object is speeding up in its rotation. The
angular acceleration is
a.
b.
c.
clockwise
counterclockwise
could be either CW or CCW
a.
b.
c.
d.
e.
3. A disk is rotation at 3 rev/s. What is the rate of
rotation in degrees/second?
a.
b.
c.
d.
6. When travelling around a banked curve, which of
these forces provides the centripetal force?
1000 degrees/second
0.008 degrees/second
20 degrees/second
2 degrees/second
I. Weight
II. Normal force
III. The speed of the car
IV. Friction
a. I
b. II & IV
c. II
d. III & IV
4. A potter's wheel moves from rest to an angular
speed of 10 rev/s in 20 s. Find its angular
acceleration in rev/s 2.
a.
b.
c.
d.
4N
20 N
12 N
8N
16 N
7. A fan blade, initially at rest, rotates with a constant
acceleration of 0.025 rad/s 2. What is the time
interval required for it to reach a 4.2-rad
displacement after starting from rest?
a. 2.0 s
b. 18 s
c. 16 s
d. 1.8 s
0.5 rev/s2
2 rev/s2
200 rev/s2
4000 rev/s2
1
9. Imagine you are a figure skater spinning as in this
figure. Estimate your moment of inertia.
8. Consider a point on a spinning wheel rotating with
rad
α = 0 2 . Which of these statements best
s
describes the linear velocity of the point?
a. the linear velocity is the same as the angular
velocity
b. the linear velocity is changing constantly
c. the linear velocity equals α
d. the linear velocity does not change
a.
b.
c.
d.
5 kg m2
50 kg m2
500 kg m2
5000 kg m2
10. Consider this figure of a rod rotating about the axis labeled “C.” The mass of the rod is 3.0 kg. What is the net
torque?
a.
b.
36 Nm clockwise
40 Nm clockwise
c.
d.
10 Nm counterclockwise
80 Nm clockwise
2
13. This figure shows 3 levers of the same length.
Each holds up a block of mass m. List the 3 levers
in order of the force required to hold up the block,
from greatest F to least F.
11. For the previous question, what is the magnitude of
the angular acceleration of the bar?
a.
b.
c.
d.
400 rad/s2
10 rad/s2
3 rad/s2
8 rad/s2
12. What is the moment of inertia for this arrangement
of particles that are attached to a central rod with
massless rods?
a.
b.
c.
d.
a.
b.
c.
d.
1, 2, 3
3, 1, 2
2, 1, 3
1, 3, 2
14. Which of the following systems is not in rotational
equilibrium?
a. A ball spinning in place at a constant angular
velocity
b. A figure skater spinning faster and faster on ice
c. A top spinning in place at a constant speed
about its center of mass
d. A seesaw balanced motionless by two children
16 kg m2
9 kg m2
10 kg m2
18 kg m2
15. These 4 wrenches have forces of the same magnitude applied to them in the direction of the arrow. Which
experiences the greatest torque, and which experiences the least torque?
a.
b.
(3) has the greatest torque.
(2) has the least torque.
(4) has the greatest torque.
(1) has the least torque.
c.
d.
(2) has the greatest torque.
(4) has the least torque.
(3) has the greatest torque.
(4) has the least torque.
3
16. This figure shows the human arm. The forearm rotates about the elbow (point O), and the biceps exerts a force on
the ulna at 0.03 m from the elbow. The total length of the forearm and hand is 0.35 m. What force must the
biceps exert in order for this arm to hold the bowling ball (whose weight is 50. N) steady (i.e. in equilibrium)?
(Assume the bicep exerts a force that is perpendicular to the forearm.)
a.
b.
220 N
580 N
c.
d.
50 N
18 N
17. What are the units for moment of inertia?
a.
b.
c.
d.
N·m
kg m
kg m/s
kg m2
4
20. A 1.0 kg ball is attached to a string that is 2.0 m
long. The ball spins at a constant angular speed of
4 rev/s. The string is lengthened to 4.0 m without
applying any additional torque to the ball. What is
the new angular speed of the ball?
18. A ventilation fan with a moment of inertia of 0.034
kg⋅m2 has a net torque of 0.11 N⋅m applied to it. If
it starts from rest, what kinetic energy will it have
8.0 s later?
a.
b.
c.
d.
a.
b.
c.
d.
2 rev/s
8 rev/s
16 rev/s
1 rev/s
21. A 10.0-kg cylinder rolls without slipping on a
rough surface. At an instant when its center of
gravity has a speed of 10.0 m/s, determine the
rotational kinetic energy about its center of gravity.
6.6 J
31 J
11 J
17 J
19. The rotational inertia of a disk about its axis is 0.70
kg m2. When a 2.0-kg weight is added to
its rim, 0.40 m from the axis, the rotational inertia
becomes:
a.
b.
c.
d.
a.
b.
c.
d.
e.
1.0 kg m2
0.70 kg m2
0.54 kg m2
0.86 kg m2
0.38 kg m2
5
750 J
250 J
500 J
1000 J
ID: A
Quiz 4--PHYS 101-3T--F13
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
TOP:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
C
PTS: 1
A
PTS: 1
A
PTS: 1
A
PTS: 1
E
PTS: 1
B
PTS: 1
B
PTS: 1
DIF: 2
7.2 Rotational Motion Under Constant Angular Acceleration
B
PTS: 1
A
PTS: 1
B
PTS: 1
B
PTS: 1
D
PTS: 1
C
PTS: 1
B
PTS: 1
D
PTS: 1
B
PTS: 1
D
PTS: 1
C
PTS: 1
DIF: 3
TOP: 8.6 Rotational Kinetic Energy
A
PTS: 1
D
PTS: 1
B
PTS: 1
1