Physics 111 Fall 2008 Exam 3 Nov. 21, 2008 Name ________________________________
B
00 cm. If the s pool contains 62.8 m of thr ead, how many A s pool of thr ead has an aver age r adius of 1.
A point on the r im of a 0.25 - m-r adius r otating wheel has a centr ipetal acceler ation of 4.0 m/s 2 . What is its angular s peed af ter this 7-s inter val? A Fer r is wheel, r otating initially at an angular s peed of 0.50 r ad/s , acceler ates over a 7.0
A 0.12- m-r adius gr inding wheel takes 5.5 s to s peed up f r om 2.0 r ad/s to 11.0 r ad/s . What is the wheel's
1. A 0.12-m-radius grinding wheel takes 5.5 s to speed up from 2.0 rad/s to 3.5.0 rad/s. What is the wheel's average angular acceleration?
a. 9.6 rad/s 2 b. c.
4.8 rad/s 2
1.6 rad/s 2 d. e.
0.33 rad/s 2
0.27 rad/s 2
2. A spool of thread has an average radius of 1.00 cm. If the spool contains 398.8 m of thread, how many turns of thread are on the spool? a. b. c. d.
100
1 000
3 140
62 800
66 900 e.
3. A Ferris wheel, rotating initially at an angular speed of 0.50 rad/s, decelerates over a 7.0-s interval at a rate of
0.040 rad/s 2 . What is its angular speed after this 7-s interval? a. b. c. d.
0.22 rad/s
0.30 rad/s
0.46 rad/s
0.78 rad/s
0.85 rad/s e.
4. A point on the rim of a 0.4-m-radius rotating wheel has a centripetal acceleration of 4.0 m/s 2 . What is the angular speed of the wheel? a. 1.0 rad/s b.
c. d. e.
2.0 rad/s
3.2 rad/s
4.0 rad/s
4.5 rad/s
5. A 3.0-m rod is pivoted about its left end. A force of 6.0 N is applied perpendicular to the rod at a distance of 1.0 m from the pivot causing a ccw torque, and a force of 8.2 N is applied at the end of the rod 3.0 m from the pivot.
The 8.2 N is at an angle of 30 o a.
15 N·m b. 0 N·m
to the rod and causes a cw torque. What is the net torque about the pivot? c. d.
-6.3 N·m
-0.6 N·m
6.3 N·m e.
6. Masses are distributed in the x,y -plane as follows: 6.0 kg at (0i + 0j) m, 4.0 kg at (2.0i + 0j) m, and 5.0 kg at
(2.0i + 3.0j) m. What is the y -coordinate of the center of gravity of this system of masses? a. 18 m b. c.
2.0 m
1.2 m d. e.
1.0 m
0.90 m

Physics 111 Fall 2008 Exam 3 Nov. 21, 2008 Name ________________________________
B
7. A disk has a moment of inertia of 3.0

10

4 kg
 m 2 and rotates with an angular speed of 3.5 rad/sec. What net torque must be applied to bring it to rest within 4.2 s? a. b. c. d. e.
4.5
7.5

10

4
3.5

10

4
5.0
2.5



10

3
10

4
10

4
N
 m
N
 m
N
 m
N
 m
N
 m
8. A rod of length L is hinged at one end. The moment of inertia as the rod rotates around that hinge is 1 /
3
ML 2 .
Suppose a 3.00-m rod with a mass of 4.00 kg is hinged at one end and is held in a horizontal position. The rod is released as the free end is allowed to fall. What is the angular acceleration as it is released? a. 3.70 rad/s 2 b. c. d. e.
7.35 rad/s 2
2.45 rad/s 2
4.90 rad/s 2
8.80 rad/s 2
9. What is the rotational inertia of a wheel that has a kinetic energy of 24400 J when rotating at 802 rev/min?
A 7 kgm2
B 12 kgm2
C 18 kgm2
D 24 kgm2
E 30 kgm2
10. A rod (mass 2.0 kg and length of 2 m) is at rest in horizontal position.
The rod falls down without a friction. What would be the rod angular velocity (in rad/s) when it was in vertical position?
A 3.1
B 2.5
C 1.4
D 3.8
E 4.7
11. Calculate the cross product of vectors A = 2i - 3j and B = 2i +2j
A 3k
B 2i-6j
C -4k
D 8k
E 2i -1j
12. The tension in the wire is 170 N. The length of the plank is 3m.
What is the torque from the tension around the point O?
A 120 Nm
B 300 Nm
C 440 Nm
D 520 Nm
E 1040 Nm

Physics 111 Fall 2008 Exam 3 Nov. 21, 2008 Name ________________________________
B
13. A uniform 100-N beam is held in a vertical position by a pin at its lower end and a cable at its upper end. A horizontal force (magnitude P) acts as shown in the figure. If P = 75 N, what is the tension in the cable? (
 net
= 0) a. 47 N b. 54 N c. 62 N d. 69 N e. 75 N
14. A 1.6 kg mass sliding on a frictionless surface has a velocity of 5.5m/s east when it undergoes a one - dimensional elastic collision with an unknown mass that is initially at rest. After the collision the velocity of the 1.6 kg mass is 1.5 m/s west. What is the unknown mass
A 2 kg
B 2.8 kg
C 3.3 kg
D 3.9 kg
E 4.7 kg
15. Three objects of masses M, 2M, and M shown are fastened to a massless rod of length L as shown. The rotational inertia about one end of the rod of this array
(see fig.) is:
A 1 /
2
ML 2
B ML 2
C 3 /
2
ML 2
D 2ML 2
E 5 /
2
ML 2 15C
16. The length of the rod shown is 4 m, force Fy = 15 N and

.
What is the magnitude of torque from the force Fy about point O?
A 25 Nm
B 33 Nm
C 39 Nm
D 46 Nm
E 57 Nm
17. A 2.5 kg rod of length 2 m with a small mass 0.5 kg attached at the end rotates about the second end with rotational velocity

= 3 rad/s. What is the kinetic energy of the rotating system?
A 24 J
B 34 J
C 45 J
D 57 J
E 68 J

Physics 111 Fall 2008 Exam 3 Nov. 21, 2008 Name ________________________________
B
1E 2d 3A 3C 4C 5D 7E 8D 9A 10D 11D 12C 13C 14B15C 16C17A