Chapter 11: Rotational Dynamics and Static Equilibrium
Practice Questions



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1.  

What condition or conditions are necessary for rotational equilibrium?
where t is torque.

2.  

What condition or conditions are necessary for translational equilibrium?

3.  

A non-zero net torque will
cause a change in angular velocity.
maintain a constant angular velocity.
cause linear acceleration.
maintain a constant angular momentum.

4.  

A zero net torque
will produce a change in angular momentum.
will conserve angular momentum.
will conserve linear momentum.
will change angular velocity.

5.  

An ice skater is in a spin with his arms outstretched. If he pulls in his arms, what happens to his rotational kinetic energy?
It increases.
It decreases.
It remains constant but non-zero.
It remains zero.

6.  

A heavy seesaw is out of balance. A lightweight girl sits on the end that is tilted downward, and a heavy boy sits on the other side so that the seesaw now balances. If the boy and girl both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw?
The side the boy is sitting on will now tilt downward.
The side the girl is sitting on will once again tilt downward.
Nothing. The seesaw will still be balanced.
It is impossible to say without knowing the masses and the distances.

7.  

A force is applied to the end of a 2 m long uniform board weighing 50 N in order to keep it horizontal, while it pushes against a wall at the left. If the angle the force makes with the board is 30° in the direction shown, the applied force F is
25 N
43.3 N
50 N
100 N

8.  

A force is applied to the end of a 2 m long uniform board weighing 50 N in order to keep it horizontal, while it pushes against a wall at the left. What is the horizontal component of the wall force?
25 N
43.3 N
50 N.
100 N

9.  

Marilyn (M) and her twin sister Sheila (S) are riding on a merry-go-round revolving at a constant rate. Sheila is half way in from the edge, as shown (bird's-eye view).

What is the relationship between the angular momentum of the two sisters?
Marilyn's is 8 times greater than Sheila's.
Marilyn's is 4 times greater than Sheila's.
Marilyn's is twice as great as Sheila's.
They are the same.

10.  

A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end). What is the magnitude of the torque exerted by the string about a horizontal axis which passes through the hinge and is perpendicular to the rod?
5 m*N
10 m*N
20 m*N
40 m*N

11.  

A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end). What is the force in the string in the previous question?
5 N
10 N
20 N
40 N

12.  

Initially, a 2.00-kg mass is whirling at the end of a string (in a circular path of radius 0.750 m) on a horizontal frictionless surface with a tangential speed of 5 m/s. The string has been slowly winding around a vertical rod, and a few seconds later the length of the string has shortened to 0.250 m. What is the instantaneous speed of the mass at the moment the string reaches a length of 0.250 m?
3.9 m/s
15 m/s
45 m/s
75 m/s

13.  

Initially, a 2.00-kg mass is whirling at the end of a string (in a circular path of radius 0.750 m) on a horizontal frictionless surface with a tangential speed of 5 m/s. The string has been slowly winding around a vertical rod, and a few seconds later the length of the string has shortened to 0.250 m. What is the final centripetal acceleration of the mass?
33.3 m/s2
100 m/s2
300 m/s2
900 m/s2

14.  

The red circle in the above 'movie' represents a person on a ladder. In which frame is the force of friction between the ladder and the ground the least? (There is no friction with the wall.)
A
B
C
D

15.  

The red circle in the above 'movie' represents a person on a ladder. At which points is the ladder most in danger of falling?
A and D
C and D
A and B
B and C

16.  

The red circle in the above 'movie' represents a person on a ladder.When is the wall force equal in magnitude to the force of friction?
A
B
C
D
All of them.

17.  

The red circle in the above 'movie' represents a person on a ladder. When is the normal force from the ground a minimum?
A
B
C
D
All of the above.

18.  

The bottom of the ladder is 1.2 m from the wall. What is the magnitude of the torque from the wall force about an axis through the bottom of the ladder?
4000 m*N
2000 m*N
600 m*N
200 m*N

19.  

The bottom of the ladder is 1.2 m from the wall. What is the magnitude of the torque from the red weight 1/3 of the way up the ladder about an axis through the bottom of the ladder?
4000 m*N
2000 m*N
600 m*N
200 m*N

20.  

What is the magnitude of the torque exerted by the F1 force on the door?
0 N-m
5 N-m
7.1 N-m
10 N-m
20 N-m

21.  

What is the magnitude of the torque exerted by the F2 force on the door?

0 N-m
5 N-m
7.1 N-m
10 N-m
20 N-m

22.  

What is the magnitude of the torque exerted by the F3 force on the door ?

0 N-m
5 N-m
7.1 N-m
10 N-m
20 N-m

23.  

What is the magnitude of the torque exerted by the F4 force on the door?

0 N-m
5 N-m
7.1 N-m
10 N-m
20 N-m

24.  

What is the magnitude of the torque exerted by the F5 force on the door?

0 N-m
5 N-m
7.1 N-m
10 N-m
20 N-m

25.  

A bicycle is travelling North. The direction of the angular momentum vector of its front wheel is
North.
East.
South.
West.


Practice Questions: Practice Questions by Carl Adler, East Carolina University. ©2002 by Prentice Hall, Inc.


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