Conservation of Angular Momentum

A person sits on a freely spinning lab stool that has no friction in its axle. When this person extends her arms,

• her moment of inertia increases and her angular speed decreases.
• her moment of inertia decreases and her angular speed increases.
• her moment of inertia increases and her angular speed increases.
• her moment of inertia increases and her angular speed remains the same.

A merry-go-round spins freely when Diego moves quickly to the center along a radius of the merry-go-round. As he does this, it is true to say that

• the moment of inertia of the system increases and the angular speed increases.
• the moment of inertia of the system decreases and the angular speed remains the same.
• the moment of inertia of the system decreases and the angular speed decreases.
• the moment of inertia of the system decreases and the angular speed increases.

A uniform solid cylinder with a radius of 10 cm and a mass of 3.0 kg is rotating about its center with an angular speed of 33.4 rpm. What is its kinetic energy? (Hint: I=1/2 MR²⁾

• 0.092 J

• 17 J

• 1.1 J

• 0.18 J

Which of these gives rotational kinetic energy?

• a
• b

What does this formula measure?

• moment of inertia
• impulse
• electric current
• angular momentum

According to the Law of Conservation of Angular Momentum, if I (momentum of inertia) increases, what will happen to ω?

• Decrease
• Stay the same
• Increase

Two children, Ahmed and Saleh, ride on a merry-go-round. Ahmed is at a greater distance from the axis of rotation than Saleh. Which of the following are true statements? 

• Saleh and Ahmed have the same tangential speed.
• Ahmed has a greater tangential speed than Saleh.
• Saleh has a greater angular speed than Ahmed.
• Saleh has a smaller angular speed than Ahmed.

When submitted to a net torque of 6.2 Nm, the

wheel of a scooter increases its angular speed from 1.4 rad/s to 4.7 rad/s in 4.5 s. What is the rotational inertia of the wheel?

• 2.2 N.m²

• 3.8 N.m²

• 4.5 N.m²

• 8.5 N.m²

The angular momentum of an object changes from 9.0 𝑘𝑔𝑚!/𝑠 to 6.0 𝑘𝑔𝑚!/𝑠 in 10 s. What is the torque causing the change?

• 0.3 Nm

• 1.3Nm

• 2.5Nm

• 4.1Nm

A windmill has an initial angular momentum 𝑜𝑓 8500 𝑘𝑔𝑚!/𝑠. The wind picks up, and 5.86 𝑠 later the windmill’s angular momentum is 9700 𝑘𝑔𝑚!/𝑠. What was the torque acting on the windmill, assuming it was constant during this time?

• 100 N.m

• 200 N.m

• 250 N.m

• 280 N.m