ConcepTest 7.1a
Bonnie and Klyde I
Bonnie sits on the outer rim of a
merry-go-round, and Klyde sits
midway between the center and the
rim. The merry-go-round makes
one complete revolution every two
seconds.
Klyde’s angular velocity is:
a) same as Bonnie’s
b) twice Bonnie’s
c) half of Bonnie’s
d) 1/4 of Bonnie’s
e) four times Bonnie’s
w
Klyde
Bonnie
ConcepTest 7.1a
Bonnie and Klyde I
Bonnie sits on the outer rim of a
merry-go-round, and Klyde sits
midway between the center and the
rim. The merry-go-round makes
one complete revolution every two
seconds.
Klyde’s angular velocity is:
a) same as Bonnie’s
b) twice Bonnie’s
c) half of Bonnie’s
d) 1/4 of Bonnie’s
e) four times Bonnie’s
The angular velocity w of any point
w
on a solid object rotating about a
fixed axis is the same. Both Bonnie
& Klyde go around one revolution
Klyde
(2p radians) every two seconds.
Bonnie
ConcepTest 7.1b
Bonnie and Klyde II
Bonnie sits on the outer rim of a merrygo-round, and Klyde sits midway
between the center and the rim. The
merry-go-round makes one revolution
every two seconds. Who has the larger
linear (tangential) velocity?
a) Klyde
b) Bonnie
c) both the same
d) linear velocity is
zero for both of them
w
Klyde
Bonnie
ConcepTest 7.1b
Bonnie and Klyde II
Bonnie sits on the outer rim of a merrygo-round, and Klyde sits midway
between the center and the rim. The
merry-go-round makes one revolution
every two seconds. Who has the larger
linear (tangential) velocity?
a) Klyde
b) Bonnie
c) both the same
d) linear velocity is zero
for both of them
Their linear speeds v will be
w
different since v = Rw and
Bonnie is located further out
(larger radius R) than Klyde.
1
VKlyde  VBonnie
2
Klyde
Bonnie
ConcepTest 7.2
Truck Speedometer
Suppose that the speedometer of
a truck is set to read the linear
a) speedometer reads a higher
speed of the truck, but uses a
speed than the true linear speed
device that actually measures the
b) speedometer reads a lower speed
angular speed of the tires. If
than the true linear speed
larger diameter tires are mounted
on the truck instead, how will that c) speedometer still reads the true
affect the speedometer reading as
linear speed
compared to the true linear speed
of the truck?
ConcepTest 7.2
Truck Speedometer
Suppose that the speedometer of
a truck is set to read the linear
a) speedometer reads a higher
speed of the truck, but uses a
speed than the true linear speed
device that actually measures the
b) speedometer reads a lower speed
angular speed of the tires. If
than the true linear speed
larger diameter tires are mounted
on the truck instead, how will that c) speedometer still reads the true
affect the speedometer reading as
linear speed
compared to the true linear speed
of the truck?
The linear speed is v = wR. So when the speedometer measures
the same angular speed w as before, the linear speed v is actually
higher, because the tire radius is larger than before.
ConcepTest 7.3a
Angular Displacement I
An object at rest begins to rotate with
a constant angular acceleration. If
this object rotates through an angle q
in the time t, through what angle did it
rotate in the time 1/2 t?
a) 1/2 q
b) 1/4 q
c) 3/4 q
d) 2 q
e) 4 q
ConcepTest 7.3a
Angular Displacement I
An object at rest begins to rotate with
a constant angular acceleration. If
this object rotates through an angle q
in the time t, through what angle did it
rotate in the time 1/2 t?
a) 1/2 q
b) 1/4 q
c) 3/4 q
d) 2 q
e) 4 q
The angular displacement is q = 1/2 at 2 (starting from rest), and
there is a quadratic dependence on time. Therefore, in half the
time, the object has rotated through one-quarter the angle.
ConcepTest 7.3b
Angular Displacement II
An object at rest begins to rotate
with a constant angular acceleration.
If this object has angular velocity w
at time t, what was its angular
velocity at the time 1/2 t?
a) 1/2 w
b) 1/4 w
c) 3/4 w
d) 2 w
e) 4 w
ConcepTest 7.3b
Angular Displacement II
An object at rest begins to rotate
with a constant angular acceleration.
If this object has angular velocity w
at time t, what was its angular
velocity at the time 1/2t?
a) 1/2 w
b) 1/4 w
c) 3/4 w
d) 2 w
e) 4 w
The angular velocity is w = at (starting from rest), and there is a
linear dependence on time. Therefore, in half the time, the
object has accelerated up to only half the speed.
The fan blade is slowing down.
What are the signs of
a.
b.
c.
d.
The fan blade is slowing down.
What are the signs of
a.
b.
c.
d.
A wheel rotating at the rate of 5 rev/s
has what approximate angular
velocity?
a) 3.2 rad/s
b) 1.6 rad/s
c) 16 rad/s
d) 31 rad/s
A wheel rotating at the rate of 5 rev/s
has what approximate angular
velocity?
a) 3.2 rad/s
b) 1.6 rad/s
c) 16 rad/s
d) 31 rad/s
Consider a child who is swinging. As
she reaches the lowest point in her
swing
a) the tension in the rope is
equal to her weight.
b) the tension in the rope is
equal to her mass times her
acceleration.
c) her acceleration is downward
at 9.8 m/s2.
d) none of these choices will
occur.
Consider a child who is swinging. As
she reaches the lowest point in her
swing
a) the tension in the rope is
equal to her weight.
b) the tension in the rope is
equal to her mass times her
acceleration.
c) her acceleration is downward
at 9.8 m/s2.
d) none of these choices will
occur.
A rigid object is rotating with an angular speed ω <
0. The angular velocity vector ω and the angular
acceleration vector α are antiparallel. The angular
speed of the rigid object is
a) clockwise and increasing
b) clockwise and decreasing
c) counterclockwise and increasing
d) counterclockwise and decreasing
A rigid object is rotating with an angular speed ω<0. The
angular velocity vector ω and the angular acceleration
vector α are antiparallel. The angular speed of the rigid
object is
a) clockwise and increasing
b) clockwise and decreasing
c) counterclockwise and increasing
d) counterclockwise and decreasing
The fact that ω is negative indicates that we are dealing with an
object that is rotating in the clockwise direction. We also know
that when ω and α are antiparallel, ω must be decreasing – the
object is slowing down. Therefore, the object is spinning more
and more slowly (with less and less angular speed) in the
clockwise, or negative, direction.