El. Suppose that a merry-go-round is rotating at the rate of 10 rev/min. a. Express this rotational velocity in rev/s. b. Express this rotational velocity in rad's. ion KPM. time of E3. Suppose that a disk rotates through five revolutions in 4 seconds. a. What is its displacement in radians in this time? b. What is its average rotational velocity in rad/s? The p ound increases at a ES. A bicycle wheel is rotationally accelerated at the constant rate of 1.2 rev/s². a. If it starts from rest, what is its rotational velocity after 4 s? b. Through how many revolutions does it turn in this time? E6. T acceleration of the disk? E7. Starting from rest, a merry-go-round accelerates at a con- stant rate of 0.2 rev/s². a. What is its rotational velocity after 5 s? b. How many revolutions occur during this time? E EL

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Chapter1: Units, Trigonometry. And Vectors
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F
166
Chapter 8 Rotational Motion of Solid Objects
exercises
EI Suppose that a merry-go-round is rotating at the rate of
10 rev/min.
a. Express this rotational velocity in rev/s.
b. Express this rotational velocity in rad/s.
E2 11
ion
time or
E3. Suppose that a disk rotates through five revolutions in
4 seconds.
a. What is its displacement in radians in this time?
b. What is its average rotational velocity in rad/s?
The
RPM.
round increases at a
ES. A bicycle wheel is rotationally accelerated at the constant
rate of 1.2 rev/s².
24 cm
a. If it starts from rest, what is its rotational velocity after 4 s?
b. Through how many revolutions does it turn in this time?
E6. T
acceleration of the disk?
E7. Starting from rest, a merry-go-round accelerates at a con-
stant rate of 0.2 rev/s².
a. What is its rotational velocity after 5 s?
b. How many revolutions occur during this time?
E8.
A force of 50 Nic applied at the end of a wranch handle that
50 N
alf-
E8 Diagram
E9. A weight of 30 N is located a distance of 10 cm from the
fulcrum of a simple balance beam. At what distance from
the fulcrum should a weight of 20 N be placed on the oppo-
site side in order to balance the system?
El
EII. Two forces are applied to a merry-go-round with a radius
of 1.2 m as shown in the diagram below. One force has
magnitude of 80 N and the other a magnitude of 50 N.
a. What is the torque about the axle of the merry-go-round
due to the 80-N force?
b. What is the torque about the axle due to the 50-N force?
c. What is the net torque acting on the merry-go-round?
E12.
E
1.2 m
50 N
O
0.2 kg
E11 Diagram
E13. A wheel with a rotational inertia of 5.6 kg-m² accelerates
at a rate of 3.0 rad/s². What net torque is needed to produce
this acceleration?
80 N
Axis
WE
-el?
inclu
E15. Two 0.2-kg masses are located at either end of a 1-m long.
very light and rigid rod as in the diagram. What is the rota
tional inertia of this system about an axis through the center
of the rod?
1m
E15 Diagram
0.2 kg
Vs
Transcribed Image Text:F 166 Chapter 8 Rotational Motion of Solid Objects exercises EI Suppose that a merry-go-round is rotating at the rate of 10 rev/min. a. Express this rotational velocity in rev/s. b. Express this rotational velocity in rad/s. E2 11 ion time or E3. Suppose that a disk rotates through five revolutions in 4 seconds. a. What is its displacement in radians in this time? b. What is its average rotational velocity in rad/s? The RPM. round increases at a ES. A bicycle wheel is rotationally accelerated at the constant rate of 1.2 rev/s². 24 cm a. If it starts from rest, what is its rotational velocity after 4 s? b. Through how many revolutions does it turn in this time? E6. T acceleration of the disk? E7. Starting from rest, a merry-go-round accelerates at a con- stant rate of 0.2 rev/s². a. What is its rotational velocity after 5 s? b. How many revolutions occur during this time? E8. A force of 50 Nic applied at the end of a wranch handle that 50 N alf- E8 Diagram E9. A weight of 30 N is located a distance of 10 cm from the fulcrum of a simple balance beam. At what distance from the fulcrum should a weight of 20 N be placed on the oppo- site side in order to balance the system? El EII. Two forces are applied to a merry-go-round with a radius of 1.2 m as shown in the diagram below. One force has magnitude of 80 N and the other a magnitude of 50 N. a. What is the torque about the axle of the merry-go-round due to the 80-N force? b. What is the torque about the axle due to the 50-N force? c. What is the net torque acting on the merry-go-round? E12. E 1.2 m 50 N O 0.2 kg E11 Diagram E13. A wheel with a rotational inertia of 5.6 kg-m² accelerates at a rate of 3.0 rad/s². What net torque is needed to produce this acceleration? 80 N Axis WE -el? inclu E15. Two 0.2-kg masses are located at either end of a 1-m long. very light and rigid rod as in the diagram. What is the rota tional inertia of this system about an axis through the center of the rod? 1m E15 Diagram 0.2 kg Vs
E16
its opprette
con or use system!
E17. A uniform disk with a mass of 4 kg and a radius of 0.3 m is
rotating with a rotational velocity of 20 rad/s
a. What is the rotational inertia of the disk? (See fig. 8.15.)
b. What is the angular momentum of the disk?
SP2
synthesis problems
SPI. A merry-go-round in the park has a radius of 1.8 m and a
rotational inertia of 900 kg-m². A child pushes the merry-
go-round with a constant force of 80 N applied at the edge
and parallel to the edge. A frictional torque of 12 N-m acts
at the axle of the merry-go-round.
and
What is the net torque acting on the merry-go-round
about its axle?
b. What is the rotational acceleration of the merry-go-
round?
c. At this rate, what will the rotational velocity of the
merry-go-round be after 15 s if it starts from rest?
d. What is the rotational acceleration of the merry-go-
round if the child stops pushing after 15 s? How long
will it take for the merry-go-round to stop turning?
off
AL
M
3 m
dock
he plank
Treat all
vity of the
boy move
1m1
g?
on without falling in
SP2 Diagram
SP). In the park, several children with a total mass of 240 kg are
riding on a merry-go-round that has a rotational inertia of
1500 kg-m² and a radius of 2.2 m. The average distance of
the children from the axle of the merry-go-round is 2.0 m
initially, since they are all riding near the edge.
E18.
t
h
in
the
Synthesis problems 167
a. What is the rotational inertia of the children about the
axle of the merry-go-round? What is the total rotational
inertia of the children and the merry-go-round?
b. The children now move inward toward the center of the
merry-go-round so that their average distance from the
axle is 0.5 m. What is the new rotational inertia for the
system?
c. If the initial rotational velocity of the merry-go-round
was 1.2 rad/s, what is the rotational velocity after the
children move in toward the center, assuming that the
frictional torque can be ignored? (Use conservation of
angular momentum.)
d. Is the merry-go-round rotationally accelerated during
this process? If so, where does the accelerating torque
come from?
SP4. A student sitting on a stool that is free to rotate, but is initially
at rest, holds a bicycle wheel. The wheel has a rotational
velocity of 6 rev/s about a vertical axis, as shown in the dia-
gram. The rotational inertia of the wheel is 2 kg m² about its
center and the rotational inertia of the student and wheel and
stool about the rotational axis of the stool is 5 kg-m².
a. What are the magnitude and direction of the initial
angular momentum of the system?
b. If the student flips the axis of the wheel, reversing
the direction of its angular-momentum vector, what is
the rotational velocity (magnitude and direction) of the
student and the stool about their axis after the wheel is
flipped? (Hint: See fig. 8.23.)
c. Where does the torque come from that accelerates the
student and the stool? Explain.
2
SP4 Diagram
Transcribed Image Text:E16 its opprette con or use system! E17. A uniform disk with a mass of 4 kg and a radius of 0.3 m is rotating with a rotational velocity of 20 rad/s a. What is the rotational inertia of the disk? (See fig. 8.15.) b. What is the angular momentum of the disk? SP2 synthesis problems SPI. A merry-go-round in the park has a radius of 1.8 m and a rotational inertia of 900 kg-m². A child pushes the merry- go-round with a constant force of 80 N applied at the edge and parallel to the edge. A frictional torque of 12 N-m acts at the axle of the merry-go-round. and What is the net torque acting on the merry-go-round about its axle? b. What is the rotational acceleration of the merry-go- round? c. At this rate, what will the rotational velocity of the merry-go-round be after 15 s if it starts from rest? d. What is the rotational acceleration of the merry-go- round if the child stops pushing after 15 s? How long will it take for the merry-go-round to stop turning? off AL M 3 m dock he plank Treat all vity of the boy move 1m1 g? on without falling in SP2 Diagram SP). In the park, several children with a total mass of 240 kg are riding on a merry-go-round that has a rotational inertia of 1500 kg-m² and a radius of 2.2 m. The average distance of the children from the axle of the merry-go-round is 2.0 m initially, since they are all riding near the edge. E18. t h in the Synthesis problems 167 a. What is the rotational inertia of the children about the axle of the merry-go-round? What is the total rotational inertia of the children and the merry-go-round? b. The children now move inward toward the center of the merry-go-round so that their average distance from the axle is 0.5 m. What is the new rotational inertia for the system? c. If the initial rotational velocity of the merry-go-round was 1.2 rad/s, what is the rotational velocity after the children move in toward the center, assuming that the frictional torque can be ignored? (Use conservation of angular momentum.) d. Is the merry-go-round rotationally accelerated during this process? If so, where does the accelerating torque come from? SP4. A student sitting on a stool that is free to rotate, but is initially at rest, holds a bicycle wheel. The wheel has a rotational velocity of 6 rev/s about a vertical axis, as shown in the dia- gram. The rotational inertia of the wheel is 2 kg m² about its center and the rotational inertia of the student and wheel and stool about the rotational axis of the stool is 5 kg-m². a. What are the magnitude and direction of the initial angular momentum of the system? b. If the student flips the axis of the wheel, reversing the direction of its angular-momentum vector, what is the rotational velocity (magnitude and direction) of the student and the stool about their axis after the wheel is flipped? (Hint: See fig. 8.23.) c. Where does the torque come from that accelerates the student and the stool? Explain. 2 SP4 Diagram
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