Physics Chapters 9 thru 11 (Due December 18; Test December 19)
Multiple Choice
Identify the choice that best completes the statement or answers the question.
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1. Which has greater linear speed, a horse near the outside rail of a merry-go-round or a horse near the inside
rail?
a. The inside horse
b. The outside horse
c. Neither—they both have the same linear speed.
2. Which has greater angular speed, a horse near the outside rail of a merry-go-round or a horse near the inside
rail?
a. Neither—they both have the same angular speed.
b. The inside horse
c. The outside horse
3. Which of the following is NOT a unit of rotational speed?
a. Meters per second
b. Revolutions per minute
c. Revolutions per second
d. Rotations per second
e. Rotations per minute
4. What is the direction of the force that acts on clothes in the spin cycle of a washing machine?
a. Inward
b. Down
c. Outward
d. Up
5. A tin can whirled on the end of a string moves in a circle because
a. the can continually pulls on the string.
b. once the can starts moving, that is its natural tendency.
c. there is a force on the can pulling it outward.
d. there is an inward force acting on the can.
e. all of the above
6. If you whirl a tin can on the end of a string and the string suddenly breaks, the can will
a. fly directly away from you.
b. fly off, tangent to its circular path.
c. fly directly toward you.
d. spiral in toward your hand.
e. spiral away from your hand.
7. A ladybug rests on the bottom of a tin can that is being whirled horizontally on the end of a string. Since the
ladybug, like the can, moves in a circle, there must be a force on it. What exerts this force?
a. Gravity
b. The string
c. There is no force acting on it.
d. The can
e. Your hand
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8. People in the future may well live inside a rotating space structure that is more than 2 km in diameter. Inside
the structure, people on the inside of the outer edge will experience 1 g while people halfway to the axis will
experience
a. 2 g.
b. 1 g.
c.
g.
d.
g.
9.
____ 10.
____ 11.
____ 12.
____ 13.
____ 14.
____ 15.
e. 0 g.
"Centrifugal forces" are an apparent reality to observers in a reference frame that is
a. rotating.
b. an inertial reference frame.
c. moving at constant velocity.
d. at rest.
e. none of the above
A person weighs less at the equator than at the poles. The reason for this has to do with the
a. tidal bulges.
b. influence of the sun, moon, and all the planets.
c. higher temperature at the equator, and expansion of matter.
d. spin of the Earth.
e. none of the above
As the rotational speed of a space habitat increases, the weight of people inside
a. decreases.
b. increases.
c. stays the same.
A car travels in a circle with constant speed. The net force on the car
a. is zero because the car is not accelerating.
b. is directed forward, in the direction of travel.
c. is directed toward the center of the curve.
d. none of the above
If Earth rotated more slowly about its axis, your weight would
a. decrease.
b. increase.
c. stay the same.
To weigh less in the Northern Hemisphere, you should go
a. west.
b. east.
c. south.
d. north.
A possible space habitat of the future is a cylinder in space rotating about its long axis. What is the relative
gravitational field along the axis of the habitat?
a. One-quarter g
b. One-half g
c. Three-quarters g
d. g
e. Zero
____ 16. When a railroad train rounds a banked track, the centripetal force needed comes not from friction, but from
the
a. vertical component of the normal force.
b. horizontal component of the normal force.
c. normal force.
d. none of the above
____ 17. The centripetal force exerted on stunt motorcyclist Biker Bob while riding on the inner vertical surface of a
circular track is
a. friction.
b. his weight.
c. the normal force.
d. none of the above
____ 18. Nellie Newton swings a rock into a circular path while holding an attached string overhead. The string makes
a 45-degree angle to the vertical (comprising a "conical pendulum"). The centripetal force that holds the rock
in its circular path is the
a. vertical component of the string tension.
b. horizontal component of the string tension.
c. tension in the string.
d. none of the above
____ 19. Stunt motorcyclist Biker Bob rides his bike inside a futuristic rotating space station-a giant rotating donutshaped structure in space. The normal support force feels like weight to him. As he rides his bike in the same
direction that the station rotates, the normal force
a. remains unaffected.
b. increases.
c. decreases.
____ 20. Stunt motorcyclist Biker Bob rides his bike inside a futuristic rotating space station—a giant rotating donutshaped structure in space. The normal support force feels like weight to him. As he rides his bike in the
opposite direction to the station’s rotation, the normal force
a. remains unaffected.
b. increases.
c. decreases.
____ 21. Suzie Spacewalker hovers in space beside a rotating space station in outer space. Both she and the center of
mass of the space station are at relative rest. If the space station is in Earth orbit, then Suzie
a. is also in Earth orbit.
b. is not in Earth orbit.
c. may or may not be in Earth orbit.
____ 22. A space habitat is designed so that the variation in g between a person's head and feet is less than 0.01 g. If
the person is 2 m tall, then the radius of the habitat is
a. 20 m.
b. 200 m.
c. 2000 m.
d. more than 2000 m.
____ 23. A game room in a rotating space habitat is located in a 0.25-g region. If a person can jump 0.5-m high in a 1-g
region, how high can the same person jump in the game room?
a. 0.5 m
b. 2 m
c. 4 m
d. 8 m
e. More than 8 m
____ 24. Where is the center of gravity of a softball bat located?
a. Exactly halfway along the bat
b. In the thin handle
c. In the more massive end of the bat
____ 25. When a wrench is slid spinning over a frictionless tabletop, its center of gravity follows
a. a regular straight-line path.
b. a wobbly path with irregular speed.
c. a straight-line path with irregular speed.
____ 26. The center of gravity of an object can be located by
a. balancing it above your finger.
b. looking at the intersection of lines drawn straight down from suspension points.
c. all of the above
d. none of the above
____ 27. In which of the following is the center of gravity located at a point where there is no mass?
a. Pineapple
b. Cookie
c. Glass of milk
d. Donut
e. Apple
____ 28. An object will fall over if its center of gravity is
a. outside the object.
b. too low.
c. not over its area of support.
d. too high.
____ 29. When you carry a heavy load with one arm, why do you tend to hold your free arm away from your body?
a. To change the mass of your body
b. To be ready to grab something in case you fall
c. To look good
d. To change the center of gravity of your body and the load
e. To change the weight of your body and the load
____ 30. If an object is in unstable equilibrium, any displacement will
a. raise its center of gravity.
b. increase its mass.
c. neither raise nor lower its center of gravity.
d. lower its center of gravity.
e. decrease its mass.
____ 31. If an object is in stable equilibrium, any displacement will
a. raise its center of gravity.
b. neither raise nor lower its center of gravity.
c. decrease its mass.
d. increase its mass.
e. lower its center of gravity.
____ 32. If an object is in neutral equilibrium, any displacement will
a. raise its center of gravity.
b. decrease its mass.
c. increase its mass.
d. neither raise nor lower its center of gravity.
e. lower its center of gravity.
____ 33. If you try to touch your toes while standing flat against a wall, you probably will fall over. The reason this
happens is that
a. your center of gravity is not located directly above your support area.
b. your center of gravity is outside your support area.
c. both A and B
____ 34. The center of mass of the solar system
a. varies as the planets move.
b. is at the center of the sun.
c. neither A nor B
____ 35. The long heavy tail of a spider monkey enables the monkey to easily vary its
a. center of gravity.
b. weight.
c. momentum.
d. inertia.
e. none of the above
____ 36. The center of mass of a human body is located at a point
a. that changes as a person bends over.
b. that is fixed, though different for different people.
c. that is always directly behind the belly button.
d. none of the above
____ 37. An object thrown into the air with a spin rotates about its
a. geometric center.
b. center of gravity.
c. edge.
d. midpoint.
e. none of the above
____ 38. If a plumb line is dropped from a suspension point of a rectangular sheet of plywood,
a. half the mass of the wood will be on either side of the line.
b. the line will pass through the center of gravity of the wood.
c. half the weight will be on either side of the line.
d. all of the above
e. none of the above
____ 39. A fish suspended in water is in what kind of equilibrium?
a. Neutral
b. Stable
c. Unstable
____ 40. A ball resting on the floor is in what kind of equilibrium?
a. Neutral
b. Stable
c. Unstable
____ 41. A picture hangs on a wall from a wire that is passed over a supporting nail. The picture is in stable
equilibrium because
a. its center of gravity is directly below the supporting nail.
b. any slight push will raise its center of gravity.
c. after any small push, it will return to its original position.
d. all of the above
____ 42. Based on stability concepts, you would expect a very broad tree to have
a. exceptionally strong roots.
b. very deep roots.
c. a very broad root system.
____ 43. You push a table tennis ball beneath the surface of water in a glass of water. The center of gravity of the glass
of water
a. rises.
b. falls.
c. neither rises nor falls.
____ 44. Torque is defined as _____.
a. mass times velocity
b. force times lever arm
c. momentum times radius
d. force times time
e. mass times acceleration
____ 45. Suppose you try loosening a nut with a wrench, and the nut doesn't give at all. You increase your chance of
success if you _____.
a. have a friend help you pull on the wrench
b. be sure to exert force perpendicular to the lever arm
c. exert a larger force
d. extend the lever arm
e. all of the above
____ 46. If a football is kicked so the force on the ball is through its center of gravity, the ball will _____.
a. tumble end over end in the air
b. not even get into the air
c. spin about its axis in the air
d. move without any tumbling or spinning
e. deflate
____ 47. The resistance an object has to changes in its rotational state of motion is called rotational _____.
a. inertia
b. momentum
c. torque
d. acceleration
e. velocity
____ 48. Which has more rotational inertia, a bicycle wheel or a solid disk of the same mass and diameter?
a. The wheel.
b. The disk.
c. They both have the same rotational inertia.
____ 49. Which has more rotational inertia, a girl running with her legs bent or the same girl running with her legs
straight?
a. With straight legs.
b. With bent legs.
c. Both have the same rotational inertia.
____ 50. Which objects roll down an incline with the greatest acceleration?
a. Objects with large rotational inertia.
b. Objects with small rotational inertia.
c. Acceleration is independent of rotational inertia in this case.
____ 51. Any solid cylinder will roll down an incline with greater acceleration than any hollow cylinder if the _____.
a. diameter of the solid cylinder is large
b. mass of the solid cylinder is small
c. mass of the solid cylinder is large
d. none of the above are necessary
____ 52. A person's rotational inertia is least about _____.
a. an axis through the person's feet
b. the person's median axis
c. the person's longitudinal axis
d. an axis through the person's hands
e. the person's transverse axis
____ 53. When a gymnast moves from an extended position to a tucked position, she _____.
a. increases her rotational inertia
b. decreases her rotational inertia
c. neither A nor B
____ 54. Angular momentum is defined as _____.
a. momentum times rotational velocity
b. mass times velocity
c. rotational inertia times linear velocity
d. none of the above
____ 55. An object will maintain its angular momentum unless acted on by an unbalanced force.
a. Always true
b. Sometimes true
c. Always false
____ 56. When an ice skater pulls in his hands to turn faster _____.
a. angular momentum must be conserved
b. his moment of inertia changes
c. his rotational speed changes
d. all of the above
____ 57. 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.
____ 58. Suppose a huge rotating cloud of particles in space gravitates together to form a dense ball. As the cloud
shrinks in size it rotates _____.
a. faster
b. slower
c. at the same speed
____ 59. Two people sit on a balanced seesaw. When one person leans toward the center of the seesaw, that person's
end of the seesaw will _____.
a. fall
b. rise
c. stay at the same level
____ 60. To turn a stubborn screw, it is best to use a screwdriver that has a _____.
a. yellow color
b. wide handle
c. long handle
d. none of the above
____ 61. Suppose a carnival Ferris wheel has seats that are located halfway between the center and the outside rim.
Compared to the ordinary Ferris wheel, where the seats are on the outside rim, your rotational speed on this
Ferris wheel would be _____.
a. greater
b. the same
c. smaller
____ 62. Which rolls to the bottom of a hill sooner, a car tire alone or the same tire mounted on a rim?
a. The mounted tire, provided the tire is more massive than the rim
b. The tire alone, provided it is as heavy as the rim
c. The mounted tire, provided the tire is lighter in weight than the rim
d. The tire alone, regardless of its weight
e. The mounted tire, regardless of its weight
____ 63. A ring and a disk roll down a hill together. Which reaches the bottom first?
a. Both reach the bottom at the same time
b. Depends on the moments of inertia
c. The disk
d. Depends on the masses
e. The ring
____ 64. A good explanation of why a ball gains speed as it rolls down an incline involves the _____.
a. force that acts on it
b. friction between it and the incline
c. torque that acts on it
d. concentrated rotational inertia of the ball
e. all of the above
____ 65. At the health spa, Felix Flex finds that pulleys on the exercise machines are not circular, but are cams—ovalshaped pulleys. At different orientations, the cams provide different _____.
a. lengths of lever arms
b. forces required to produce a given torque
c. both A and B
d. none of the above
____ 66. A common thread spool rests on a flat table. You gently pull in a horizontal direction on a short piece of
thread wrapped around the spool. The spool will roll toward you _____.
a. whether the string is wound over or under the spool
b. only if the string is wound under the bottom of the spool spindle
c. only if the string is wound over the top of the spool spindle
____ 67. A common thread spool rests on a flat table. You gently pull at an angle on a short piece of thread wrapped
around the spool, which causes the spool to slide without rotating. With the thread at this angle, the lever arm
is _____.
a. perpendicular to the applied force
b. small, but not zero, and the torque is zero
c. small and the torque is also small
d. none of the above
____ 68. A meter stick is balanced at the 50.0-cm mark. You tie a 10.0-N weight at the 15.0-cm mark. Where should a
30.0-N weight be placed so the meter stick will again be balanced?
a. 10.0-cm mark
b. 15.0-cm mark
c. 61.7-cm mark
d. 25.0-cm mark
e. 30.0-cm mark
____ 69. A 3-kg ball is whirled on the end of a string that is 2 m long. The ball's linear speed is 4 m/s. What is its
angular momentum?
a. 2 kg·m·m/s
b. 6 kg·m·m/s
c. 8 kg·m·m/s
d. 24 kg·m·m/s
e. 48 kg·m·m/s
____ 70. A ring, a disk, and a solid ball having equal masses roll down a hill at the same time. Which reaches the
bottom first?
a. Depends on what each is made of.
b. The disk
c. The ring
d. Depends on the radius of each.
e. The ball
True/False
Indicate whether the statement is true or false.
____ 71. The rotational speed of a wheel is defined as the number of rotations it makes in a unit of time.
____ 72. Any force that causes an object to move in a circular path is called a centripetal force.
____ 73. It is possible to rotate a very large cylindrical space habitat around its central axis at just the right speed so
people living inside the cylinder will experience a force that feels like gravity.
____ 74. A bug on a turning phonograph record will make more turns per minute if it is located toward the center of the
record.
____ 75. When you whirl a can on the end of a string, the centripetal force on the can is actually the pull of the string
on the can.
____ 76. Ladybugs on the inside of a spinning bicycle tire can experience a force that feels like gravity to them.
____ 77. The point located at the center of an object's mass distribution is called the object's center of mass.
____ 78. When an object is balanced so that a displacement raises its center of gravity, the object is said to be in neutral
equilibrium.
____ 79. When an object is balanced so that a displacement lowers its center of gravity, the object is said to be in stable
equilibrium.
____ 80. When an object is balanced so that a displacement neither raises nor lowers its center of gravity, the object is
said to be in neutral equilibrium.
____ 81. Even though a baseball bat spins and wobbles when thrown in the air, its center of gravity follows a smooth
parabolic path.
____ 82. The center of mass of an object is always located at the object's geometric center.
____ 83. An unaided object will topple over when its center of gravity extends beyond its support base.
____ 84. Torque is the product of a force exerted on an object times the lever arm.
____ 85. Rotational inertia is the resistance an object has to changes in its rotational state.
____ 86. In order for a seesaw to be in rotational equilibrium, the sum of the torques acting on it need not be balanced
if one person sits closer to the fulcrum than the other person.
____ 87. If you kick a football through its center of gravity, it will tumble as it sails through the air.
____ 88. In order to increase his or her rotational inertia, a tightrope walker can carry a long stick.
____ 89. A short pendulum has more rotational inertia than a long pendulum of the same mass.
____ 90. Gymnasts change their rotational inertia while going through gymnastic routines.
____ 91. Ice skaters can increase their spin rate by using the conservation of angular momentum.
Problem
92. The tangential speed at the outer rim of a Ferris wheel is 10 m/s. What is the tangential speed of a position
half way from the center to the outer rim?
93. You sit at the outer rim of a Ferris wheel that rotates at 2 revolutions per minute (RPM). What would your
rotational speed be if you were instead clinging to a position halfway from the center to the outer rim?
94. A vertical pole standing against a wall topples to the ground and the center of the pole has a speed of 13 m/s
as it hits. With what speed does the far end of the pole hit the ground?
95. Tapered rims on railroad-train wheels enable a train to round curves without any wheel skidding. Consider a
curve where the outer track is one part in 50 longer than the inner track. The wide part of the rim should have
a diameter wider than the narrow part by at least one part in
96. At the outer edge of a rotating space habitat, 130 m from its center, the rotational acceleration is g. What is
the rotational acceleration at a distance of 65 m from the center of the habitat?
97. Suppose the torque produced by a wrench on a stubborn nut is 30 N·m. If the lever arm is doubled with no
change in force, what is the resulting torque?
98. A 40-kg boy sits on a seesaw 2.0 m from the fulcrum. What distance from the fulcrum should a 30-kg girl sit
in order to balance the seesaw?
99. Consider a long uniform wooden plank of weight W resting on a table. The left end of the plank can extend
beyond the table without toppling as long as the CG of the plank rests on the table. If the CG extends beyond
the table's edge, then a weight placed on its right end can prevent toppling. How much weight would prevent
toppling if of the plank extended beyond the edge?
100. A ball at the end of a long rope is swung in a horizontal circular path. The rope is then pulled in so that the
1
radius of the path is 2 as big. How does the tangential speed of the ball change?