Rotating Systems: Energy & Momentum
A closed system is rotating with a certain angular momentum. If there are no external torques acting on the system, what happens to the total angular momentum of the system?
It increases.
It decreases.
It remains constant.
It oscillates.
A figure skater is spinning with her arms extended. She then pulls her arms in towards her body. What happens to her angular speed?
It increases.
It decreases.
It remains constant.
It becomes zero.
A complex mechanical system consists of multiple rotating parts with varying moments of inertia and angular speeds. One part increases its moment of inertia while another part decreases its moment of inertia such that the total moment of inertia of the system remains constant. However, an internal motor transfers energ...
The total angular momentum increases.
The total angular momentum decreases.
The total angular momentum remains constant.
The total angular momentum oscillates.
A spinning top experiences a constant torque of 2 \text{ N} \cdot \text{m}
for 3 \text{ s}
. If its initial angular momentum was 4 \text{ kg} \cdot \text{m}^2/ ext{s}
, what is its final angular momentum?
2 \text{ kg} \cdot \text{m}^2/ ext{s}
6 \text{ kg} \cdot \text{m}^2/ ext{s}
10 \text{ kg} \cdot \text{m}^2/ ext{s}
12 \text{ kg} \cdot \text{m}^2/ ext{s}
Under what condition is the angular momentum of a system conserved?
When the net external force on the system is zero.
When the net external torque on the system is zero.
When the system is isolated and not interacting with its surroundings.
When the moment of inertia of the system is constant.
A system consists of two particles rotating about a common axis. Particle A has an angular momentum of 2L
and particle B has an angular momentum of . What is the total angular momentum of the system?
3L
0
A spinning wheel has a constant angular momentum. If a small external torque is applied to the wheel, what will happen to its angular momentum?
The angular momentum will increase.
The angular momentum will decrease.
The angular momentum will remain constant.
The angular momentum will oscillate.

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A torque of 10 \text{ N} \cdot \text{m}
is applied to a rotating object for 5 \text{ s}
. What is the angular impulse?
2 \text{ kg} \cdot \text{m}^2/ ext{s}
50 \text{ kg} \cdot \text{m}^2/ ext{s}
0.5 \text{ kg} \cdot \text{m}^2/ ext{s}
5 \text{ kg} \cdot \text{m}^2/ ext{s}
A star collapses, decreasing its radius. As a result, its moment of inertia decreases. Assuming no external torques act on the star, how does its angular speed change?
The angular speed increases.
The angular speed decreases.
The angular speed remains constant.
The angular speed becomes zero.
A rotating disk collides with a stationary ring. After the collision, they stick together and rotate as a single unit. Which of the following is true about the system's angular momentum and kinetic energy?
Both angular momentum and kinetic energy are conserved.
Angular momentum is conserved, but kinetic energy is not.
Kinetic energy is conserved, but angular momentum is not.
Neither angular momentum nor kinetic energy is conserved.