A student sits on a rotating stool holding two 2.3-kg objects. When his arms are

Question

A student sits on a rotating stool holding two 2.3-kg objects. When his arms are extended horizontally, the objects are 1.0 m from the axis of rotation and he rotates with an angular speed of 0.75 rad/s. The moment of inertia of the student plus stool is 3.0 kg m2 and is assumed to be constant. The student then pulls in the objects horizontally to 0.40 m from the rotation axis. (a) Find the new angular speed of the student. rad/s (b) Find the kinetic energy of the student before and after the objects are pulled in. before J after J

Explanation / Answer

MI = 3 + 2* 2.3 = 7.6 L = 7.6 * 0.75 New MI = 3 + 4.6 * 0.5^2 = 4.15 New "w" = 7.6 * 0.75 / 4.15 = 1.37 rad/s KE before = 1/2 * 7.6 * 0.75^2 = 2.13 J KE after = 1/2 * 4.15 * 1.37^2 = 3.9 J

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