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In this lesson, we will learn how to calculate the rotational kinetic energy of an object from its moment of inertia and other kinematic properties.

Q1:

A neutron star of mass 2 . 0 0 × 1 0 3 0 kg and radius 10.0 km rotates with a period of 0.02000 seconds. What is its rotational kinetic energy?

Q2:

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?

Q3:

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⋅m^{2}, what is the rotational kinetic energy of the forearm?

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