Deck 8: Rotational Motion

Question 1

Toss a baseball bat into the air and it wobbles about its

A)geometrical center.
B)center of mass.
C)heavier end.

Answer 1

center of mass.

Question 2

Your pet hamster sits on a record player whose angular speed is constant.If he moves to a point twice as far from the center,then his linear speed

A)doubles.
B)halves.
C)remains the same.

Answer 2

doubles.

Question 3

Horses that move with the fastest linear speed on a merry-go-round are located

A)near the center.
B)near the outside.
C)anywhere,because they all move at the same speed.

Answer 3

near the outside.

Question 4

A broom is easier to balance on its end when the heavier end (the brush end)is

A)nearest your hand.
B)highest,farthest from your hand.
C)same either way

Question 5

The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is

A)above a place of support.
B)relatively low for such a tall building.
C)stabilized by its structure.
D)displaced from its center.
E)in the same place as its center of mass.

Question 6

An industrial flywheel has a greater rotational inertia when most of its mass is

A)nearest the rim.
B)nearest the axis.
C)uniformly spread out as in a disk.

Question 7

If a turntable's rotational speed is doubled,then the linear speed of a pet hamster sitting on the edge of the record will

A)double.
B)halve.
C)remain the same.

Question 8

The tapered shape of the parts of the wheels that ride on railroad tracks allows opposite wheels to

A)in effect,vary their diameters.
B)travel at different linear speeds for the same rotational speed.
C)Both A and B are correct.

Question 9

Which moves faster in m/s on a merry-go-round: a horse on the inside or a horse on the outside near the outer rail?

A)inside horse
B)outside horse
C)Both move at the same speed in m/s.

Question 10

The long,heavy tail of a spider monkey enables the monkey to easily vary its

A)weight.
B)momentum.
C)inertia.
D)center of gravity.
E)none of these

Question 11

Suppose the circumference of a bicycle wheel is 2 meters.If it rotates at 1 revolution per second when you are riding the bicycle,then your speed will be

A)1 m/s.
B)2 m/s.
C)3 m/s.
D)3)14 m/s.
E)6)28 m/s.

Question 12

When a train makes a curve,different parts of the wheel rims

A)cover a different distance in the same time.
B)must all expand at the same time.
C)must all contract at the same time.
D)vibrate at different rates.

Question 13

A torque acting on an object tends to produce

A)equilibrium.
B)rotation.
C)linear motion.
D)velocity.
E)a center of gravity.

Question 14

The rotational inertia of your leg is greater when your leg is

A)straight.
B)bent.
C)same either way

Question 15

Put a pipe over the end of a wrench when trying to turn a stubborn nut on a bolt,to effectively make the wrench handle twice as long,you'll multiply the torque by

A)two.
B)four.
C)eight.

Question 16

The center of mass of a human body is located at a point

A)that is fixed,but different for different people.
B)that is always directly behind the belly button.
C)that changes as a person bends over.
D)none of these

Question 17

A coin and a ring roll down an incline starting at the same time.The one to reach the bottom first will be the

A)ring.
B)coin.
C)Both reach the bottom at the same time.

Question 18

On a balanced seesaw,a boy three times as heavy as his partner sits

A)1/3 the distance from the fulcrum.
B)less than 1/3 the distance from the fulcrum.
C)more than 1/3 the distance from the fulcrum.

Question 19

Since each rolling wheel of a railroad train is tapered,the narrow part of the wheel has a tangential speed that is

A)greater than that of the wide part.
B)smaller than that of the wide part.
C)the same as that of the wide part.

Question 20

Consider a string with several rocks tied along its length at equally spaced intervals.You whirl the string overhead so that the rocks follow circular paths.Compared to a rock in the middle of the string,a rock at the outer end moves

A)half as fast.
B)twice as fast.
C)at the same linear speed.

Question 21

To turn a stubborn screw,it is best to use a screwdriver that has a

A)wide handle.
B)long handle.
C)smooth handle.
D)none of these

Question 22

To kick a football so it won't topple end over end,kick it so the force of impact extends

A)above its center of gravity.
B)through its center of gravity.
C)below its center of gravity.

Question 23

A 1-kg rock is suspended from the tip of a meter stick at the 0-cm mark so that the meter stick balances like a seesaw when the fulcrum is at the 25-cm mark.From this information,what is the mass of the meter stick?

A)1/4 kg
B)1/2 kg
C)3/4 kg
D)1 kg
E)more than 1 kg

Question 24

A person weighs less at the equator than at the poles.The main reason for this has to do with

A)the spin of the Earth.
B)the shape of the Earth.
C)the influence of the sun,moon,and all the planets.
D)the law of action and reaction.

Question 25

The chef at the infamous Fattening Tower of Pizza tosses a spinning disk of uncooked pizza dough into the air.The disk's diameter increases during the flight,while its rotational speed

A)remains constant.
B)increases.
C)decreases.

Question 26

When a twirling ice skater brings her arms inward,her rotational speed

A)increases.
B)decreases.
C)remains the same.

Question 27

If the Earth rotated more slowly about its axis,your apparent weight would

A)increase.
B)decrease.
C)stay the same.
D)be zero.

Question 28

A ball rolls down a hill mainly because of

A)an unbalanced torque.
B)a balanced torque.
C)its rotational inertia.
D)its angular acceleration.
E)its angular momentum.

Question 29

Strictly speaking,to weigh less in the Northern Hemisphere,you should move to a location further

A)north (toward the pole).
B)south (toward the equator).
C)east.
D)west.

Question 30

When doing somersaults,you'll more easily rotate when your body is

A)straight with both arms above your head.
B)straight with both arms at your sides.
C)balled up.
D)no difference

Question 31

The center of gravity of a circular disk of sheet metal is

A)at the center of the disk.
B)midway between the center and the outside.
C)two-thirds of the way between the center and the outside.
D)impossible to predict without knowing the metal density.

Question 32

Two people are balanced on a seesaw.If one person leans toward the center of the seesaw,that person's end of the seesaw will

A)rise.
B)fall.
C)stay at the same level.
D)rise and then fall.
E)fall and then rise.

Question 33

A tightrope walker more easily balances on a tightwire if his pole

A)is held high.
B)droops.
C)is short but heavy.

Question 34

Centrifugal forces are an apparent reality to observers in a reference frame that is

A)moving at constant velocity.
B)an inertial reference frame.
C)at rest.
D)rotating.
E)none of these

Question 35

Use the following figure to answer the question:
If the Earth had two identical moons in one circular orbit,and the moons were as far apart in that orbit as they could be,the center of gravity of the Earth-moons system would be

A)at the center of the Earth.
B)inside the Earth,but off center.
C)outside the Earth,but within the orbital path of the moons.
D)outside the Earth,but beyond the orbital path of the moons.

Question 36

Use the following figure to answer the question:
A carnival has a Ferris wheel where the seats are located halfway between the center and outside rim.If you were at the outside rim,your angular speed while riding on this Ferris wheel would be

A)less and your tangential speed more.
B)more and your tangential speed less.
C)the same and your tangential speed less.

Question 37

A baseball bat is balanced on a fulcrum.The center of gravity of the bat is located

A)closer to the handgrip.
B)above the fulcrum.
C)near the heavy end.

Question 38

Consider a rotating donut-shaped space habitat where living quarters are on the inside surface farthest from the axis.If the rotational speed of the habitat increases,the apparent weight of people inside

A)increases.
B)decreases.
C)stays the same.
D)is always zero.

Question 39

A car travels in a circle with constant speed.The net force on the car is

A)directed forward,in the direction of travel.
B)directed toward the center of the curve.
C)zero because the car is not accelerating.
D)none of these

Question 40

For a system in mechanical equilibrium

A)the resultant force must be zero.
B)the resultant torques must be zero.
C)the resultant forces and torques must both be zero.
D)the resultant forces and torques must be equal.

Question 41

Suppose you're on a Ferris wheel at a carnival,seated 10 m from the Ferris wheel's axis.If you make a complete rotation each minute,your linear speed is

A)10 m/min.
B)31.4 m/min.
C)62.8 m/min.
D)100 m/min.
E)Not enough information is given.

Question 42

Stand a meterstick on its end and let go and it rotates to the floor.If you attach a heavy weight to its upper end and repeat,falling time will be

A)more.
B)less.
C)the same.

Question 43

If the planet Jupiter underwent gravitational collapse,its rate of rotation about its axis would

A)decrease.
B)increase.
C)stay the same.
D)more information needed

Question 44

Suppose you put very large-diameter tires on your car.Then,your speedometer will show a speed that is

A)higher than it is actually.
B)lower than it is actually.
C)the same as before.

Question 45

Use the following figure to answer the question:
Suppose you are at the center of a large freely-rotating horizontal turntable in a carnival funhouse.As you crawl toward the edge,the angular momentum of you and the turntable

A)decreases.
B)increases.
C)remains the same,but the RPMs decrease.
D)decreases in direct proportion to your decrease in RPMs.
E)none of these

Question 46

Neglecting air resistance,which will roll from rest to the bottom of an incline first,an empty jar,or the same jar filled with peanut butter?

A)the filled jar
B)the empty jar
C)Both reach the bottom at the same time.
D)More information is needed.

Question 47

What is the simulated gravitational field strength half-way between the axis of the Earth and the outside edge where the field strength is g?

A)zero
B)g
C)one-half g
D)three-quarters g

Question 48

The gravitational field best suited for humans living in an outer space colony is

A)zero.
B)g)
C)one-quarter g.
D)one-half g.
E)three-quarters g.

Question 49

A flywheel's diameter is twice that of another of the same shape and mass.The larger flywheel's rotational inertia is

A)four times the other's.
B)two times the other's.
C)the same as the other's.
D)half the other's.

Question 50

A boy plays solitary seesaw by placing a long plank over a small rock and sitting at one end of the plank.When the seesaw is balanced,the boy's mass is most likely

A)greater than the mass of the seesaw.
B)less than the mass of the seesaw.
C)equal or very nearly equal to the mass of the seesaw.
D)Not enough information is given.

Question 51

You know that you can safely stand on the overhanging end of a heavy plank that rests on a table.How far out depends on your mass and the mass of the plank.Suppose you can stand on the end of a plank that overhangs the edge of the supporting table 1/4 its total length.Then how massive is the plank compared to your mass?

A)1/2 your mass
B)the same as your mass
C)1 1/2 times your mass
D)twice your mass
E)4 times your mass

Question 52

If you balance a broom horizontally on one finger,the center of gravity of the broom will be above your finger - closer to the bristles end than the handle end.If you saw the broom in two pieces at that point and weigh the two parts on a scale,you'll find that the heavier part is the

A)bristles part.
B)handle part.
C)both the same weight

Question 53

If the polar icecaps melted,the resulting water would spread over the entire Earth.This new mass distribution would tend to make the length of a day

A)longer.
B)shorter.
C)stay the same.
D)shorter at first,then longer.
E)longer at first,then shorter.

Question 54

A huge rotating cloud of particles in space gravitate together to form an increasingly dense ball.As it shrinks in size,the cloud

A)rotates faster.
B)rotates slower.
C)rotates at the same speed.
D)cannot rotate.

Question 55

A ring and a disk,initially at rest,roll down a hill together.The one to reach the bottom first

A)is the ring.
B)is the disk.
C)depends on the masses.
D)depends on the relative rotational inertias.
E)Both reach the bottom at the same time.

Question 56

Which will roll down an incline in the shortest time,a can filled with water or the same can filled with ice?

A)water
B)ice
C)both the same
D)Not enough information is given.

Question 57

Consider a bowling alley inside a rotating space torus (huge "donut").Compared to your bowling experience on earth,you will notice that the ball

A)feels lighter when you throw it in the direction of the moving alley,and heavier when you throw it in the opposite direction.
B)feels heavier when you throw it in the direction of the moving alley,and lighter when you throw it in the opposite direction.
C)veers to the right when you throw it in the direction of the moving alley,and to the left when you throw it in the opposite direction.
D)none of these

Question 58

A flywheel's mass is twice that of another of the same size and shape.The more massive flywheel's rotational inertia is

A)four times the other's.
B)two times the other's.
C)the same as the other's.
D)half the other's.

Question 59

A small boy places a rock under the middle of a of a long wood plank,sits near one end and his mother sits near the opposite end.To balance each other

A)the mother should move further away from the boy.
B)the boy should move closer to his mother.
C)both should move closer to the ends of the plank.
D)both should move closer to the middle of the plank.
E)None of the above choices would work.

Question 60

A ring,a disk,and a solid sphere begin rolling down a hill together.The one to reach the bottom first is the

A)ring.
B)disk.
C)sphere.
D)They all reach the bottom at the same time.
E)Not enough information is given.

Question 61

A swimming area in a rotating space habitat is located in a 1/4 g region.If a diver can jump 1 m high in a 1 g region,how high can the same diver jump in the swimming area?

A)1 m
B)2 m
C)4 m
D)16 m
E)more than 16 m