Physics 71 2nd LE Reviewer II

1.

A club-ax consists of a symmetrical 8.0-kg stone attached to the end of a uniform 2.5-kg stick that is 98 cm long. The dimensions of the club-ax are shown in the figure. How far is the center of mass from the handle end of the club ax? Note: Some portion of the stick is inserted inside the club-ax. A. B. C.

2.

19 cm 37 cm 49 cm

D. E.

79 cm 98 cm

A record is turning at a constant angular speed. A ladybug sits on the rim of the record, while a fly landed also on the record, halfway between the center and the rim. Which of the following statements is FALSE? A. B. C. D.

The ladybug is moving at a greater speed than the fly. The fly has a smaller tangential acceleration than the ladybug. The ladybug and the fly are moving at equal angular speeds. Both the ladybug and the fly experience a constant acceleration magnitude.

For the next two questions: Consider Bobby riding on the rim of a merry-go-round of radius r = 1.5 m. It is initially moving at a constant angular speed of 0.50 rad/s. He then asked Tina to push one of the bars of the merry-go-round such that his angular speed increases to 1.50 rad/s in 2.0s. 3.

What is his angular acceleration? A. B.

4.

C. D.

0.75 rad/s2 1.0 rad/s2

E.

1.5 rad/s2

E.

1.5 m/s2

What was his initial radial acceleration? A. B.

5.

0.38 rad/s2 0.50 rad/s2 0.38 m/s2 0.50 m/s2

C. D.

0.75 m/s2 1.0 m/s2

Consider a dust particle which landed on a 1.0-kg disk. The disk has radius r = 0.25 m. The disk’s angular speed increased from 1.0 rad/s to 3.0 rad/s after rotating 15 rad. Which of the following statement(s) is/are TRUE about the dust’s motion on the rim of the disk? I. The dust experiences a constant angular speed. II. The dust’s radial acceleration is constant. III. The dust’s tangential acceleration is zero when it is at the center of the disk. A. B.

6.

III only I & II only

E.

I, II, & III

Disk Solid sphere Ring

D. E.

Disk and ring They will all reach the bottom at the same time.

A solid metal ball (m = 2.0 kg, r = 0.25 m) is connected to a rigid rod of negligible mass of length L = 1.0 m. The solid metal ball is then made to rotate at an axis located at the end other end of the rod. What is the moment of inertia of the solid metal ball about this axis? (Isolidsphere= (2/5) MR2) A. B. C.

8.

C. D.

A disk, a solid sphere, and a ring of the same mass and the same radius rolled down the same inclined plane. If the three objects were released from rest at the same height at the same instant, which of the three will reach the bottom of the inclined plane first? A. B. C.

7.

I only II only

2

0.050 kg·m 0.12 kg·m2 2.0 kg·m2

D. E.

Rotation axis

1.0 m

2

3.2 kg·m 4.5 kg·m2

A disk is free to rotate about an axis. A force applied a distance d from the axis causes an angular acceleration α. What angular acceleration is produced if the same force is applied 2d from the axis? A. B.

¼α ½α

C. D.

α 2α

E.

4α

For the next two questions A 0.50-kg solid disk of radius r = 0.25 m is rolling without slipping on a horizontal floor. Its angular speed is 2.5 rad/s. (Isoliddisk= ½ MR2) 9.

What is the magnitude of the translational velocity of the center of mass of the disk? A. B.

0.25 m/s 0.62 m/s

C. D.

1.2 m/s 2.5 m/s

E.

5.0 m/s

E.

0.25 J

10. What is the rotational kinetic energy of the disk? A. B.

0.049 J 0.10 J

C. D.

0.15 J 0.20 J

11. Which of the following statements is/are TRUE? I.

If the angular velocity of an object is zero at some instant, the net torque on the object must be zero at that instant. II. The moment of inertia of an object depends on the location of the axis of rotation. III. The moment of inertia of an object depends on the angular velocity of the object.

A. B.

I only II only

C. D.

III only I & II only

E.

I, II & III

12. A 2.5-kg solid cylinder of radius 0.20 m is initially at rest. A rope of negligible mass is wrapped around it and pulled with a force of 17 N. What is the torque exerted by the rope on the cylinder? A. B.

0.050 N·m 0.15 N·m

C. D.

1.7 N·m 3.4 N·m

E.

68 N·m

13. A wheel of radius R is rolling without slipping at an angular speed ω. The velocity of the point on the rim that is in contact with the surface, relative to the surface, is ___________. A. B. C. D. E.

zero equal equal equal equal

to Rω in the direction of motion of the center of mass to Rω opposite the direction of motion of the center of mass to the velocity of the center of mass in magnitude to the velocity of the center of mass but opposite in direction

14. A solid cylinder and a solid sphere have equal masses and equal radii. Both roll without slipping on a horizontal surface. If their kinetic energies are the same, then the translational speed of the cylinder is_______________. A. B. C.

zero greater than that of the sphere less than that of the sphere

D. E.

equal that of the sphere infinite

For the next two questions

F1

2.0 N

The force F1 is applied at the midpoint of a meterstick at a 60o angle with respect to the horizontal. Force F2, on the other hand, is applied at the other end of the meter stick. 15. What is the direction of the net torque on the meter stick about the indicated rotation axis? A. B.

Into the page Out of the page

C. D.

F2

1.5 N

Rotation axis

To the left To the right

E.

Upwards

16. What is the magnitude of the net torque on the meter stick about the axis shown? A. B.

0.63 N·m 0.87 N·m

C. D.

1.0 N·m 1.5 N·m

E.

2.0 N·m

17. A constant net torque acts on a merry-go-round. The power input of the torque is _______. A. B. C. D.

Zero Constant Proportional to the angular speed of the merry-go-round Proportional to the angular acceleration of the merry-go-round

18. A particle of mass m is moving with speed v along a straight line that passes through point P. What is the angular momentum of the particle about point P? A. B. C.

mv zero depends on the distance of the particle from point P

D. E.

END OF EXAM

changes sign as the particle passes through point P depends on the distance of point P from some reference point