10.5 Angular momentum and its conservation  (Page 6/10)

Which rotational system would be best to use as a model to measure how angular momentum changes when forces on the system are changed?

1. a fishing reel
2. a planet and its moon
3. a figure skater spinning
4. a person's lower leg

You are collecting data to study changes in the angular momentum of a bicycle wheel when a force is applied to it. Which of the following measurements would be least helpful to you?

1. the time for which the force is applied
2. the radius at which the force is applied
3. the angular velocity of the wheel when the force is applied
4. the direction of the force

Which torque applied to a disk with radius 7.0 cm for 3.5 s will produce an angular momentum of 25 N•m•s?

1. 7.1 N•m
2. 357.1 N•m
3. 3.6 N•m
4. 612.5 N•m

Which of the following would be the best way to produce measurable amounts of torque on a system to test the relationship between the angular momentum of the system, the average torque applied to the system, and the time for which the torque is applied?

1. having different numbers of people push on a merry-go-round
2. placing known masses on one end of a seesaw
3. touching the outer edge of a bicycle wheel to a treadmill that is moving at different speeds
4. hanging known masses from a string that is wound around a spool suspended horizontally on an axle

The diagram above shows a top view of a child of mass M on a circular platform of mass 2 M that is rotating counterclockwise. Assume the platform rotates without friction. Which of the following describes an action by the child that will increase the angular speed of the platform-child system and why?

1. The child moves toward the center of the platform, increasing the total angular momentum of the system.
2. The child moves toward the center of the platform, decreasing the rotational inertia of the system.
3. The child moves away from the center of the platform, increasing the total angular momentum of the system.
4. The child moves away from the center of the platform, decreasing the rotational inertia of the system.

A moon is in an elliptical orbit about a planet as shown above. At point A the moon has speed uA and is at distance RA from the planet. At point B the moon has speed uB . Has the moon's angular momentum changed? Explain your answer.

A hamster sits 0.10 m from the center of a lazy Susan of negligible mass. The wheel has an angular velocity of 1.0 rev/s. How will the angular velocity of the lazy Susan change if the hamster walks to 0.30 m from the center of rotation? Assume zero friction and no external torque.

1. It will speed up to 2.0 rev/s.
2. It will speed up to 9.0 rev/s.
3. It will slow to 0.01 rev/s.
4. It will slow to 0.02 rev/s.