A student sits on a rotating stool holding two 3.5-kg objects. When his arms are
ID: 1969832 • Letter: A
Question
A student sits on a rotating stool holding two 3.5-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 0.50 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 *3.5 = 10 L = 10 * 0.75 New MI = 3 + 8 * 0.5^2 = 5 New "w" = 10 * 0.75 / 5 = 1.5 rad/s KE before = 1/2 * 10* . 0.75^2 = 2.81 J KE after = 1/2 * 5 * 1.5^2 = 5.625 J
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