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Lesson: Rotational Kinetic Energy

Worksheet: Rotational Kinetic Energy • 9 Questions


A neutron star of mass kg and radius 10.0 km rotates with a period of 0.02000 seconds. What is its rotational kinetic energy?

  • A J
  • B J
  • C J
  • D J
  • E J


A system consists of an annular cylinder of mass 1.0 kg with inner radius 20 cm and outer radius 30 cm mounted on a disk of mass 2.0 kg and radius 50 cm. The system rotates about an axis through the centers of the annular cylinder and of the disk at 10 rev/s.

What is the moment of inertia of the system?

What is the system’s rotational kinetic energy?


A baseball pitcher throws the ball in a motion where there is rotation of the forearm about the elbow joint as well as other movements. If the linear velocity of the ball relative to the elbow joint is 20.0 m/s at a distance of 0.480 m from the joint and the moment of inertia of the forearm is 0.500 kg⋅m2, what is the rotational kinetic energy of the forearm?


A uniform cylindrical grindstone has a mass of 10 kg and a radius of 12 cm.

What is the rotational kinetic energy of the grindstone when it is rotating at rpm?

After the grindstone’s motor is turned off, a knife blade is pressed against the outer edge of the grindstone with a perpendicular force of at 5.0 N. The coefficient of kinetic friction between the grindstone and the blade is 0.80. Use the work energy theorem to determine how many turns the grindstone makes before it stops.


An elevator car of mass kg is pulled 40.0 m vertically upward at constant speed by its cable. An average friction force of 100 N resists the motion of the elevator car.

What work is done on the elevator car by the cable?

What work is done on the elevator car by the force of gravity?

What is the total work done on the elevator car?