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Mixed Practice: Chapter 8/9 Rotational Motion Honors Physics
Burns
1.
a
b
c
d
An object will fall over if its center of gravity is
outside the object.
too low.
not over its area of support.
too high.
2. 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
3.
A
B
C
D
E
An object thrown into the air with a spin rotates about its
geometric center.
center of gravity.
edge.
midpoint.
none of the above
4. 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
5. At the health spa, Felix Flex finds that pulleys on the exercise machines are not circular, but are
cams—oval-shaped 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
6.
A
B
C
D
E
The resistance an object has to changes in its rotational state of motion is called rotational _____.
inertia
momentum
torque
acceleration
velocity
7. 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.
8. An object will maintain its angular momentum unless acted on by an unbalanced force.
A Always true
B Sometimes true
C Always false
9.
A
B
C
D
E
A ring and a disk roll down a hill together. Which reaches the bottom first?
Both reach the bottom at the same time
Depends on the moments of inertia
The disk
Depends on the masses
The ring
10.
A
B
C
D
E
A good explanation of why a ball gains speed as it rolls down an incline involves the _____.
force that acts on it
friction between it and the incline
torque that acts on it
concentrated rotational inertia of the ball
all of the above
11.
A
B
C
D
E
A ring, a disk, and a solid ball having equal masses roll down a hill at the same time. Which
reaches the bottom first?
Depends on what each is made of.
The disk
The ring
Depends on the radius of each.
The ball
12.
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
13. A figure skater on ice with arms extended, spins at a rate of 2.0 rev/s. After she draws her arms in,
she spins at 5 rev/s. By what factor does her moment of inertia change in the process?
A 1x
B 5/2 x
C 2/5 x
D 5x
14.
John sets up a turntable to measure velocity of a cardboard flag rotating on the circular disk.
He recorded the time it took for the 2 cm tab to pass through a photogate. At a radius of 12.3 cm,
the time it took for the flag to pass through the photogate was 0.0934 seconds. What is the
velocity at that radius?
a. 0.76 m/s
b. 21.4 m/s
c. 0.21 m/s
d. 4.67 m/s
15.
What is the angular velocity (in rad/s) at that radius?
a. 10.7 rad/s
b. 0.026 rad/s
c. 0.16 rad/s
d. 1.74 rad/s
16.
Which setting was this turntable on, in RPMs?
a. 16 RPM
b. 33 RPM
c. 45 RPM
d. 78 RPM
17.
If you make a graph of linear velocity vs. radius, what shape would you get?
a. linear (y = mx)
b. direct square (y = mx2)
c. indirect (y = 1/x)
d. indirect square (y = 1/x2)
18.
What happens to tangential velocity as the radius increases?
a. increases
b. decreases
c. stays the same
19.
What happens to angular velocity as the radius increases?
a. Increases
b. Decreases
c. Stays the same
20.
Why does the clamp at the fulcrum have no effect on the torque?
a. It's too small to matter.
b. It acts parallel to the lever arm.
c. It is at the fulcrum and therefore has no distance.
d. Its force is automatically equal to zero.
21.
Define torque.
a. Tendency of a force to cause movement.
b. A quantity of inertia.
c. Tendency of a force to balance.
d. Tendency of a force to cause rotation.
22.
What are the conditions for equilibrium?
a. The object must be at rest.
b. The object must be moving at constant speed.
c. All of the forces on the object must add up to zero.
d. All of the torques on the object must add up to zero.
e. Both a and b.
f. Both c and d.
Students Art, Bart, Cis, and Dot sit on a rotating turntable at different distances from the
center as indicated:
A. Art, m = 60 kg, sits at 1/4 r.
B. Bart, m = 25 kg, sits at 1/2 r.
C. Cis, m = 50 kg, sits at 3/4 r.
D. Dot, m = 20 kg, sits at r.
23.
Which student has the greatest angular velocity?
a. A
b. B
c. C
d. D
e. They all have the same angular velocity.
24.
From greatest to least, rank the angular momenta of the 4 students.
_____
A
_____
B
_____
C
_____
D
25.
From greatest to least, rank the linear speeds of the 4 students.
_____
A
_____
B
_____
C
_____
D
26.
If no net torque acts on the system, then angular momentum is
a. Increasing
b. Decreasing
c. Constant
d. Variable
27. With no unbalanced torques, if the rotational inertia increases, then the rotational velocity must
a. Decrease
b. Increase
c. Remain the same
d. It can do any of these, depending on the situation.
28.
When the mass of a rotating object increases, the rotational inertia _____.
a. Decrease
b. Increase
c. Remain the same
d. It can do any of these, depending on the situation.
29.
Which is easiest to rotate—when most of the mass of a system is
a. Close to the axis
b. Far from the axis
c. It could be either of these, depending on the situation.
30.
The Second Condition of Equilibrium states that if something is at rest,
a. all of the forces that cause the object to rotate clockwise must be balanced by all of the
forces that cause the object to rotate counterclockwise.
b. all of the torques that cause the object to rotate clockwise must be balanced by all of the
torques that cause the object to rotate counterclockwise.
c. all of the forces that cause the object to move up must be balanced by all of the forces
that cause the object to move down
31.
Rotational physics follows a completely different and unrelated set of rules than linear
(translational) physics.
a. True
b. False
32.
The greater the rotational inertia, the more difficult it is to change the rotational speed of an
object.
a. True
b. False
33. Where is the CG of the earth’s atmosphere?
34. Why is it dangerous to slide open the top drawers of a fully loaded file cabinet or dresser that is
not secured to the floor or wall?
35. When a car drives off a cliff, why does it rotate forward as it falls?
36. Why doesn’t the Tower of Pisa fall over?
37. How can you design objects to reduce the likelihood of tipping?
38. If you wish to have maximum speed at the very bottom of a roller coaster ride, should you sit in
a front car, a middle car, or a rear car?
39. A weight of 2 N is placed 0.2 m from the pivot of a 0.5-N beam. If the beam is 1-m long and the
pivot is in the exact center, where should you place a 1.5 N weight to balance the beam?
40. A weight of 2 N is placed 0.2 m from the pivot of a 0.5-N beam. If the beam is 1-m long and the
pivot is in the exact center, how much weight should be placed at 0.4 m from the pivot to
balance the beam?
41. A weight of 2 N is placed 0.2 m from the pivot of a 0.5-N beam. If the beam is 1-m long and the
pivot is at the 0.3-m mark, where should you place a 1.5 N weight to balance the beam?
42. A uniform bridge span weighs 50 x 103 N and is 40.0 m long. An automobile weighing 15 x 103
N is parked with its center of gravity located 12.0 m from the right pier. What upward support
force is provided by the left pier?
43. A child wants to use a 10 kg board that is 3.5 m long as a seesaw. Since all her friends are
busy, she balances the board by putting the support 1-m away from her when she sits at one
end. What is her mass?
44. A uniform board weighs 500 N and is 10.0 m long. It overhangs a building roof, extending over
the edge of the roof by 2.5 m. A paint bucket filled with sand, weighing 150 N, is sitting at the
end of the board. How far out is it safe for the 700 N worker to walk on the board? Assuming
he can stretch no more than 0.5 m, can he reach the bucket when he needs it?
45. A 1.4-kg rod is supported by a single rope at an angle of 34° over the rod to its connection
point on the wall. The rod is attached to the wall on the other side by a hinge. Assume that the
rod is uniform. (a) What is the tension in the rope? (b) What are the two components of the
support force exerted by the hinge?
46. Which is easiest to rotate—when most of the mass is close to the axis or far from the axis?
47. Consider balancing a hammer upright on the tip of your finger. If the head of the hammer is
heavy and the handle long, would it be easier to balance with the end of the handle on your
fingertip so that the head is at the top, or the other way around with the head at your fingertip
and the end of the handle at the top?
48. Consider a pair of meter sticks standing nearly upright against a wall. If you release them,
they’ll rotate to the floor in the same time. But what if one has a massive hunk of clay stuck to
its top end? Will it rotate to the floor in a longer or shorter time?
49. The Earth moves about the Sun in an elliptical orbit. As the Earth moves closer to the Sun,
does the Earth-Sun system's moment of inertia increase, decrease, or remain constant?
50. Two hoops or rings (I = MR2) are centered, lying on a phonograph record. The smaller one has
a radius of 0.05 m and the larger a radius of 0.1 m. Both have a mass of 3 kg. What is the total
moment of inertia as the record turns around? Ignore the mass of the record.
51. A majorette takes two batons and fastens them together in the middle at right angles to make
an "x" shape. Each baton was 0.8 m long and each ball on the end is 0.20 kg. (Ignore the
mass of the rods.) What is the moment of inertia if the arrangement is spun around an axis
through the center perpendicular to both rods?
52. A uniform 10-m-long , 50-N ladder rests against a smooth vertical wall. If the ladder is just on
the verge of slipping when the angle it makes with the ground is 50º, find the coefficient of
static friction between the ladder and ground?
53. A woman who weighs 500 N is standing on a board that weighs 100 N. The board is supported
at each end, and the support force at the right end is 3 times bigger than the support force at
the left end. If the board is 8 m long, how far from the right end is the woman standing?
54. A uniform 40-N board supports 2 children weighing500 N and 350 N. The support is under the
center of gravity of the board, and the 500-N child is 1.50 m from the center. A) Determine the
upward force, N, exerted on the board from the support. B) Determine where the 350-N child
should sit to balance the system.
55. A uniform, horizontal, 300-N beam, 5.00-m long, is attached to a wall by a pin connection that
allows the beam to rotate. Its far end is supported by a cable that makes an angle of 53.0 with
the horixontal. If a 600-N person stands 1.50-m from the wall, find (a) the tension in the cable
and (b) the force exerted on the beam by the wall.
56. You've climbed up to the top of a 7.5 m high telephone pole. Just as you reach the top, the
pole breaks at the base. Are you better off letting go of the pole and falling straight down, or
sitting on top of the pole and falling down to the ground on a circular path? Or does it make no
difference?
57. The total kinetic energy of a baseball thrown with a spinning motion is a function of which of
the following?
a. its linear velocity but not rotational velocity
b. its rotational velocity but not linear velocity
c. both linear and rotational velocities
d. neither linear nor rotational velocity
58. Our galaxy may have begun as a huge cloud of gas and particles. Suppose the original cloud
was far larger than the present size of the galaxy, was more or less spherical, and was rotating
very much more slowly than at present. Gravitation between particles would have pulled them
closer. What would be the role of angular momentum conservation on the galaxy’s shape and
present rotational speed?
59. A broom balances at its center of gravity. If you saw the broom into 2 parts through the center
of gravity and then weigh each part on a scale, which part will weigh more?
60. A skater, starting a spin with their arms extended, quickly pulls her arms in close to the body.
What effect does this have on the skater? Why?
61. The Earth's gravity exerts no torque on a satellite orbiting the Earth in an elliptical orbit.
Compare the motion at the point nearest the Earth (perigee) to the motion at the point farthest
from the Earth (apogee). At the point closest to the Earth
a. the angular velocity will be greatest although the linear speed will be the same.
b. the speed will be greatest although the angular velocity will be the same.
c. the kinetic energy and angular momentum will both be greater.
d. none of the above.
62. A 40 kg boy is standing on the edge of a stationary 30 kg platform that is free to rotate. The
boy tries to walk around the platform in a counterclockwise direction. As he does
a. The platform doesn't rotate.
b. The platform rotates in a clockwise direction just fast enough so that the boy remains
stationary relative to the ground.
c. The platform rotates in a clockwise direction while the boy goes around in a
counterclockwise direction relative to the ground.
d. Both go around with equal angular velocities but in opposite directions.
63. A figure skater on ice with arms extended, spins at a rate of 2.0 rev/s. After she draws her
arms in, she spins at 5 rev/s. By what factor does her moment of inertia change in the
process?