A student sits on a freely rotating stool holding two weights, eachof mass 3.00
ID: 1751268 • Letter: A
Question
A student sits on a freely rotating stool holding two weights, eachof mass 3.00 kg. When his arms are extended horizontally, theweights at 1.00 m from the axis of rotation and he rotates with anangular speed of 0.750 rad/s. The moment of inertia of the studentplus stool is 3.00 kg*m^2 and is assumed to be constant. Thestudent pulls the weights inward horizontally to a position 0.300 mfrom the rotation axis.a) Find the new angular speed of the student
b) Find the kinetic energy of the rotating system before andafter he pulls the weights inward.
a) Find the new angular speed of the student
b) Find the kinetic energy of the rotating system before andafter he pulls the weights inward.
Explanation / Answer
(a)from the given problem the total anguar momentum ofthe system of the student the stool and the weights about the axis of rotation is givenby Itotal = Iweights +Istudent = 2 (m r2) + 3.00 kg . m2 intially we get r = 1.0 m Ii = 2 (3.0 kg) (1.0 m)2 +3.00 kg . m2 = ........ kg .m2 finally r = 0.30 m If = 2 (3.0 kg) (0.30 m)2 +3.0 kg . m2 = ........ kg .m2 according to the law of conservation of momentumwe get If f =Ii i solve for f f = ........ rad / s (b) KEi = (1 / 2) Iii2 =........ J KEf = (1 / 2) Iff2 =........ J =........ J
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