Chapter 8

Question 1

Circular Motion Definition

Answer 1

When an object turns about an internal axel, it is undergoing circular motion or rotation.

Question 2

Circular Motion has two kinds of speed __.

Answer 2

tangential (linear) and rotational (circular)

Question 3

Points closer to the circumference have a higher __ than the points closer to the center.

Answer 3

tangential speed

Question 4

(symbol v) tangential speed =

Answer 4

distance traveled/ total time

Question 5

Rotational (angular) speed is the __

Answer 5

number of rotations or revolutions per unit of time (symbol ω)

Question 6

Tangential Speed =

Answer 6

Radial distance (r) x Rotational speed (ω)

Question 7

A ladybug sits halfway between the rotational axis and
the outer edge of the turntable. When the turntable has
a rotational speed of 20 RPM and the bug has a
tangential speed of 2 cm/s, what will be the rotational
and tangential speeds of her friend who sits at the outer
edge?
A. 1 cm/s
B. 2 cm/s
C. 4 cm/s
D. 8 cm/s

Answer 7

C. 4 cm/s

Question 8

Rotational Inertia (symbol I)

Answer 8

An object about an axis tends to remain rotating about the same axis and the same rotational speed unless interfered with an outside force
(an object to resist changes in
its rotational state of motion)

Question 9

Greater the distance between an object’s mass concentration and axis __.

Answer 9

the greater the rotational inertia

Question 10

A hoop and a disk are released from the top of
an incline at the same time. Which one will
reach the bottom first?
A. Hoop
B. Disk
C. Both together
D. Not enough information

Answer 10

B. Disk
Hoop has larger rotational inertia, so it will be
slower in gaining speed.

Question 11

Torque Definition

Answer 11

The tendency of a force to cause rotation.

Question 12

Torque has 3 factors

Answer 12

• Magnitude of the force
• The direction in which it acts
• The point at which it is applied on the object

Question 13

Torque Equation

Answer 13

Torque = lever arm x force

Question 14

The lever are depends on 2 things

Answer 14

• where the force is applied.
• the direction in which it acts.

Question 15

A girl sits 3m to the left and 4m down from a pivot system. She currently weights 200 N and is handed a 50N bag of apples. Where should she sit in order to remain balanced?
A. 1 m from pivot
B. 1.5 m from pivot
C. 2 m from pivot
D. 2.4 m from pivot

Answer 15

D. 2.4 m from pivot
She should exert same torque as before.
Torque = lever arm x force = 3 m x 200 N = 600 Nm
Torque = new lever arm x new force
= new lever arm x 250 N

Question 16

Centre of Mass Definition

Answer 16

The average position of all the mass that makes up the object

Question 17

Center of gravity (CG) Definition

Answer 17

The average position of weight distribution

Question 18

Centripetal Force Definition

Answer 18

Any force directed toward a fixed center

Question 19

Centripetal Force depends on 3 things

Answer 19

• mass of object.
• tangential speed of the object.
• radius of the circle.

Question 20

Centripetal Force Equation

Answer 20

(mass x tangential speed^2)/radius

Question 21

Suppose you double the speed at which you
round a bend in the curve, by what factor must
the centripetal force change to prevent you from
skidding?
A. Double
B. Four times
C. Half
D. One-quarter

Answer 21

B. Four times
Because the term for “tangential speed” is squared, if you double the tangential speed, the centripetal force will be double squared, which is four times

Question 22

Suppose you take a sharper turn than before and halve the radius, by what factor will the
centripetal force need to change to prevent
skidding?
A. Double
B. Four times
C. Half
D. One-quarter

Answer 22

A. Double
Because the term for “radius” is in the denominator, if you halve the radius, the centripetal force will double.

Question 23

Centrifugal force definition

Answer 23

An outward force that acts upon a occupant inside the rotating system

Question 24

Angular momentum Definition

Answer 24

The “inertia of rotation” of rotating objects

Question 25

Angular momentum Equation

Answer 25

rotational inertia x angular velocity or mass x tangential velocity x radius

Question 26

Suppose you are swirling a can around and suddenly decide to pull the rope in halfway; by what factor would the speed of the can change? A. Double B. Four times C. Half D. One-quarter

Answer 26

A. Double Angular momentum = mass x tangential velocity x radius Angular Momentum is proportional to radius of the turn. No external torque acts with inward pull, so angular momentum is conserved. Half radius means speed doubles.

Question 27

The law of conservation of angular momentum

Answer 27

If no external net torque acts on a rotating system, the angular momentum of that system remains constant.

Question 28

Suppose by pulling the weights inward, the rotational inertia of the man reduces to half its value. By what factor would his angular velocity change? A. Double B. Three times C. Half D. One-quarter

Answer 28

A. Double Angular momentum = rotational inertia x angular velocity. Angular momentum is proportional to "rotational inertia.“ If you halve the rotational inertia, to keep the angular momentum constant, the angular velocity would double.