ROTATIONAL MOTION

When a child folds his hands on a rotating turntable, reducing moment of inertia to 2/5 of initial, what happens to rotational kinetic energy?

• It decreases
• It remains the same
• It becomes zero
• It increases

A child stands on a rotating turntable with arms outstretched at 40 rev/min. If the child folds hands and reduces moment of inertia to 2/5 of initial, what is the new angular speed?

• 16 rev/min
• 60 rev/min
• 80 rev/min
• 100 rev/min

A solid cylinder of mass 20 kg rotates about its axis with an angular speed of 100 rad/s. The radius is 0.25 m. What is the magnitude of angular momentum?

• 12.5 kg·m²/s
• 62.5 kg·m²/s
• 125 kg·m²/s
• 31.25 kg·m²/s

A solid cylinder of mass 20 kg rotates about its axis with an angular speed of 100 rad/s. The radius is 0.25 m. What is the rotational kinetic energy of the cylinder?

• 1250 J
• 312.5 J
• 625 J
• 2500 J

Two objects, a hollow cylinder and a solid sphere, have the same mass and radius. Equal torques are applied about their respective axes of rotation. Which one will acquire a greater angular speed after a given time?

• Hollow cylinder
• Both will have same angular speed
• Solid sphere
• Cannot be determined