ConcepTest 7.1aConcepTest 7.1a Bonnie and Klyde IBonnie and Klyde I

BonnieBonnieKlydeKlyde

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 velocityangular velocity of any point

on a solid object rotating about a

fixed axis is the sameis the same. Both Bonnie

& Klyde go around one revolution

(2 radians) every two seconds.

ConcepTest 7.1aConcepTest 7.1a Bonnie and Klyde IBonnie and Klyde I

BonnieBonnieKlydeKlyde

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

ConcepTest 7.1bConcepTest 7.1b Bonnie and Klyde IIBonnie and Klyde II

BonnieBonnieKlydeKlyde

a) Klyde

b) Bonnie

c) both the same

d) linear velocity is zero for both of them

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 revolution every two seconds. Who has the larger linear (tangential) velocity?

Their linear speedslinear speeds vv will be

different since v = Rv = R and

Bonnie is located further outBonnie is located further out

(larger radius R) than Klyde.

BonnieBonnie

KlydeKlyde

BonnieKlyde V21

V

a) Klyde

b) Bonnie

c) both the same

d) linear velocity is zero

for both of them

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 revolution every two seconds. Who has the larger linear (tangential) velocity?

ConcepTest 7.1bConcepTest 7.1b Bonnie and Klyde IIBonnie and Klyde II

Suppose that the speedometer of a truck is set to read the linear speed of the truck, but uses a device that actually measures the angular speed of the tires. If larger diameter tires are mounted on the truck instead, how will that affect the speedometer reading as compared to the true linear speed of the truck?

a) speedometer reads a higher speed than the true

linear speed

b) speedometer reads a lower speed than the true linear speed

c) speedometer still reads the true linear speed

ConcepTest 7.2 ConcepTest 7.2 Truck SpeedometerTruck Speedometer

Suppose that the speedometer of a truck is set to read the linear speed of the truck, but uses a device that actually measures the angular speed of the tires. If larger diameter tires are mounted on the truck instead, how will that affect the speedometer reading as compared to the true linear speed of the truck?

a) speedometer reads a higher speed than the true

linear speed

b) speedometer reads a lower speed than the true linear speed

c) speedometer still reads the true linear speed

The linear speed is v = R. So when the speedometer measures

the same angular speed as before, the linear speed v is actually

higher, because the tire radius is larger than before.

ConcepTest 7.2 ConcepTest 7.2 Truck SpeedometerTruck Speedometer

An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle in the time t, through what angle did it rotate in the time 1/2 t?

a) 1/2

b) 1/4

c) 3/4

d) 2

e) 4

ConcepTest 7.3aConcepTest 7.3a Angular Displacement IAngular Displacement I

An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle in the time t, through what angle did it rotate in the time 1/2 t?

a) 1/2

b) 1/4

c) 3/4

d) 2

e) 4

The angular displacement is = 1/2 t 2 (starting from rest), and

there is a quadratic dependence on time. Therefore, in half the half the

timetime, the object has rotated through one-quarter the angleone-quarter the angle.

ConcepTest 7.3aConcepTest 7.3a Angular Displacement IAngular Displacement I

An object at rest begins to rotate with a constant angular acceleration. If this object has angular velocity at time t, what was its angular velocity at the time 1/2 t?

a) 1/2

b) 1/4

c) 3/4

d) 2

e) 4

ConcepTest 7.3bConcepTest 7.3b Angular Displacement IIAngular Displacement II

An object at rest begins to rotate with a constant angular acceleration. If this object has angular velocity at time t, what was its angular velocity at the time 1/2t?

a) 1/2

b) 1/4

c) 3/4

d) 2

e) 4

The angular velocity is = t (starting from rest), and there is a

linear dependence on time. Therefore, in half the timehalf the time, the

object has accelerated up to only half the speedhalf the speed.

ConcepTest 7.3bConcepTest 7.3b Angular Displacement IIAngular Displacement II

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 A wheel rotating at the rate of 5 rev/s has what approximate angular has what approximate angular velocity?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 A wheel rotating at the rate of 5 rev/s has what approximate angular has what approximate angular velocity?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 Consider a child who is swinging. As she reaches the lowest point in her she reaches the lowest point in her swingswing

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 Consider a child who is swinging. As she reaches the lowest point in her she reaches the lowest point in her swingswing

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 A rigid object is rotating with an angular speed ωω < < 0. The angular velocity vector 0. The angular velocity vector ωω and the angular and the angular acceleration vector acceleration vector αα are antiparallel. The angular are antiparallel. The angular speed of the rigid object isspeed 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 A rigid object is rotating with an angular speed ωω<0. The <0. The angular velocity vector angular velocity vector ωω and the angular acceleration and the angular acceleration vector vector αα are antiparallel. The angular speed of the rigid are antiparallel. The angular speed of the rigid object isobject 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.