Rotating Systems: Energy & Momentum
A small ball is thrown past a fixed point. Which of the following changes would increase the ball's angular momentum about that point?
Decreasing the mass of the ball.
Decreasing the velocity of the ball.
Increasing the distance between the point and the ball's path.
Making the ball pass closer to the point.
A projectile is launched and its angular momentum is calculated with respect to the launch point. How does the projectile's angular momentum change during its flight?
It remains constant because gravity is a conservative force.
It increases as the projectile gains height.
It decreases as the projectile loses horizontal velocity.
It changes due to the changing angle and distance from the launch point.
A graph of torque vs. time for a rotating object is shown below. The graph is a rectangle with a constant torque of 10 Nm from t = 0 to t = 4 seconds. What is the angular impulse applied to the object?
10 Nms
20 Nms
40 Nms
80 Nms
An object experiences an angular impulse of 50 kg cdot m^2/s
. If its initial angular momentum was 20 kg cdot m^2/s
, what is its final angular momentum?
20 kg cdot m^2/s
30 kg cdot m^2/s
50 kg cdot m^2/s
70 kg cdot m^2/s
A 0.5 kg ball is moving at 4 m/s. At a specific instant, it is 2 meters away from a reference point, and the angle between its velocity vector and the line connecting it to the reference point is 90 degrees. What is the angular momentum of the ball with respect to the reference point at that instant?
2 kg cdot m^2/s
4 kg cdot m^2/s
8 kg cdot m^2/s
16 kg cdot m^2/s
A constant torque of 20 Nm is applied to a rotating object for 5 seconds. What is the angular impulse?
4 Nms
25 Nms
100 Nms
400 Nms
A complex torque vs. time graph requires integration to find the angular impulse. What does the integral of torque with respect to time represent?
The average torque
The change in angular velocity
The angular impulse
The final angular momentum

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The slope of an angular momentum vs. time graph represents what physical quantity?
Angular displacement
Angular velocity
Net torque
Moment of inertia
Two disks are rotating about the same axis. Disk A has a moment of inertia and angular velocity . Disk B has a moment of inertia 2I
and angular velocity . If the two disks are brought into contact and rotate together, what is the total angular momentum of the system?
2I\omega
4I\omega
A figure skater is spinning with her arms extended. If she suddenly pulls her arms in closer to her body, what happens to her angular velocity?
Her angular velocity decreases.
Her angular velocity remains the same.
Her angular velocity increases.
Her moment of inertia increases.