Chapter 8
Rotational Motion
To impress his friends while riding on a
carnival
Ferris wheel, Prankster Paul gets out of his
chair and climbs along the spoke of the wheel
toward its center while the wheel continues in
uniform motion. While climbing toward the center,
Paul’s linear speed
a.
b.
c.
d.
increases while his angular speed remains
unchanged.
decreases while his angular speed remains
unchanged.
and his angular speed increase.
and his angular speed decrease.
To impress his friends while riding on a
carnival
Ferris wheel, Prankster Paul gets out of his
chair and climbs along the spoke of the wheel
toward its center while the wheel continues in
uniform motion. While climbing toward the center,
Paul’s linear speed
a.
b.
c.
d.
increases while his angular speed remains
unchanged.
decreases while his angular speed remains
unchanged.
and his angular speed increase.
and his angular speed decrease.
When you roll a tapered cup across
a table, the path of the cup curves
because the wider end rolls
a. slower.
b. at the same speed as the narrow part.
c. faster.
d. in an unexplained way.
When you roll a tapered cup across
a table, the path of the cup curves
because the wider end rolls
a. slower.
b. at the same speed as the narrow part.
c. faster.
d. in an unexplained way.
The rotational inertia of an object is
greater when most of the mass is
located
a. near the center.
b. away from the rotational axis.
c. on the rotational axis.
d. off-center.
The rotational inertia of an object is
greater when most of the mass is
located
a. near the center.
b. away from the rotational axis.
c. on the rotational axis.
d. off-center.
For round objects rolling down an
incline, the fastest objects are generally
those with the
a. greatest rotational inertia compared with mass.
b. lowest rotational inertia compared with mass.
c. most streamlining for reduced air drag.
d. highest center of gravity.
For round objects rolling down an
incline, the fastest objects are generally
those with the
a. greatest rotational inertia compared with mass.
b. lowest rotational inertia compared with mass.
c. most streamlining for reduced air drag.
d. highest center of gravity.
Which of these will roll down an
incline fastest?
a.
b.
c.
d.
Disk
Hoop
Solid ball
The one with the greatest mass will roll fastest.
Which of these will roll down an
incline fastest?
a.
b.
c.
d.
Disk
Hoop
Solid ball
The one with the greatest mass will roll fastest.
A torque is a force
a. like any other force.
b. multiplied by a lever arm.
c. that is fictitious.
d. that accelerates things.
A torque is a force
a. like any other force.
b. multiplied by a lever arm.
c. that is fictitious.
d. that accelerates things.
When two children of different
weights balance on a seesaw, they
each produce
a. equal torques.
b. unequal torques.
c. equal-magnitude torques in opposite directions.
d. equal forces.
When two children of different
weights balance on a seesaw, they
each produce
a. equal torques.
b. unequal torques.
c. equal-magnitude torques in opposite directions.
d. equal forces.
The center of mass of a donut
is located
a. in the hole.
b. in material making up the donut.
c. near the center of gravity.
d. over a point of support.
The center of mass of a donut
is located
a. in the hole.
b. in material making up the donut.
c. near the center of gravity.
d. over a point of support.
The center of gravity of an object
a. lies inside the object.
b. lies outside the object.
c. may or may not lie inside the object.
d. is near the center of mass.
The center of gravity of an object
a. lies inside the object.
b. lies outside the object.
c. may or may not lie inside the object.
d. is near the center of mass.
An object resting on a surface will
topple over if its center of gravity
a. lies outside the object.
b. extends beyond the support base.
c. is displaced from its center of mass.
d. lowers at the point of tipping.
An object resting on a surface will
topple over if its center of gravity
a. lies outside the object.
b. extends beyond the support base.
c. is displaced from its center of mass.
d. lowers at the point of tipping.
The center of gravity of your best
friend is located
a. near the belly button.
b. at different places depending on body
orientation.
c. near the center of mass.
d. at a fulcrum when rotation occurs.
The center of gravity of your best
friend is located
a. near the belly button.
b. at different places depending on body
orientation.
c. near the center of mass.
d. at a fulcrum when rotation occurs.
When an stable object is made to
topple over, its center of gravity
a. is at first raised.
b. is at first lowered.
c. plays a minor role.
d. plays no role.
When an stable object is made to
topple over, its center of gravity
a. is at first raised.
b. is at first lowered.
c. plays a minor role.
d. plays no role.
Which more accurately describes
what happens in the circular spin cycle
of a washing machine?
a. Water is forced away from the clothes.
b. Clothes are forced into a circular path while
water is not.
c. Centripetal force acts on the water but not the
clothes.
d. Centrifugal force acts on the clothes but not the
water.
Which more accurately describes
what happens in the circular spin cycle
of a washing machine?
a. Water is forced away from the clothes.
b. Clothes are forced into a circular path while
water is not.
c. Centripetal force acts on the water but not the
clothes.
d. Centrifugal force acts on the clothes but not the
water.
When you whirl a tin can in a horizontal
circle overhead, the force that holds the
can in the circular path acts in a direction
a. inward.
b. outward.
c. either inward or outward.
d. parallel to the force of gravity.
When you whirl a tin can in a horizontal
circle overhead, the force that holds the
can in the circular path acts in a direction
a. inward.
b. outward.
c. either inward or outward.
d. parallel to the force of gravity.
When you whirl a tin can in a horizontal
circle overhead, the force that the can
exerts on the string acts in a direction
a. inward.
b. outward.
c. either inward or outward.
d. parallel to the force of gravity.
When you whirl a tin can in a horizontal
circle overhead, the force that the can
exerts on the string acts in a direction
a. inward.
b. outward.
c. either inward or outward.
d. parallel to the force of gravity.
Explanation: The string pulls on the can, action; in reaction,
the can pulls on the string in the opposite direction.
A bug inside a can whirled in a circle
feels a force of the can on its feet. This
force acts in a direction
a. toward the center of the circular path.
b. away from the center of the circular path.
c. either toward or away from the center of the
circular path.
d. parallel to the force of gravity.
A bug inside a can whirled in a circle
feels a force of the can on its feet. This
force acts in a direction
a. toward the center of the circular path.
b. away from the center of the circular path.
c. either toward or away from the center of the
circular path.
d. parallel to the force of gravity.
Explanation: This is the support force of the floor on the
bug’s feet, equal and opposite to the fictitious centrifugal
force on the bug. If this is confusing, be kind to yourself.
It also confuses the best of students.
Gravity can be simulated for
astronauts in outer space if
their habitat
a. is very close to Earth.
b. is in free fall about Earth.
c. rotates.
d. revolves about Earth.
Gravity can be simulated for
astronauts in outer space if
their habitat
a. is very close to Earth.
b. is in free fall about Earth.
c. rotates.
d. revolves about Earth.
For an object traveling in a circular
path, its angular momentum doubles
when its
a. linear speed doubles and radius remains the
same.
b. radius doubles and its linear speed remains the
same.
c. mass doubles and linear speed and radius
remain the same.
d. All of these.
For an object traveling in a circular
path, its angular momentum doubles
when its
a. linear speed doubles and radius remains the
same.
b. radius doubles and its linear speed remains the
same.
c. mass doubles and linear speed and radius
remain the same.
d. All of these.
Explanation: The equation mvr guides the answer. Double
either m, v, or r and angular momentum is doubled.
The angular momentum of a system
is conserved
a. never.
b. under some conditions.
c. under all conditions.
d. when angular velocity remains unchanged.
The angular momentum of a system
is conserved
a. never.
b. under some conditions.
c. under all conditions.
d. when angular velocity remains unchanged.
Explanation: A condition for angular momentum being
conserved is that no net torque acts on the system.
Steady angular velocity and changing radial distance
produce changing angular momentum, so choice d is
incorrect.
As Earth’s daily rotation decreases due
to tidal friction, the Moon undergoes
a.
b.
c.
d.
a decrease in angular momentum.
an increase in angular momentum.
wobbling in its orbit about Earth.
None of these.
As Earth’s daily rotation decreases due
to tidal friction, the Moon undergoes
a.
b.
c.
d.
a decrease in angular momentum.
an increase in angular momentum.
wobbling in its orbit about Earth.
None of these.
Explanation: Angular momentum of the Earth–Moon system
is conserved. So a decrease in angular momentum of
Earth due to tidal friction (an internal force or torque) is
accompanied by an increase in angular momentum of
the Moon (an increase in distance from Earth).