A student holds two leadweights, each ofmass 11 kg. When the students’arms are e

Question

A student holds two leadweights, each ofmass

11 kg. When the students’arms are extended

horizontally, the lead weightsare 0.98 m from

the axis of rotation and thestudent rotates

with an angular speed of1.9rad/sec. The

moment of inertia of studentplus stool is

5.5 kgm2 and is assumed to be constant; i.e.,

the student’s arms are massless! Thenthe

student pulls the lead weightshorizontally to

a radius 0.22 m from the axis ofrotation.

Calculate the final angularspeed of the

system. Answer in units ofrad/s.

Explanation / Answer

m = 22 kg, r1 = .98 m, r2 = .22 m,1 = 1.9 rad/s, I = 5.5 kg(m2) Angular momentum is conserved: L1 = L2 I11 =I22 (I + mr12)1 = (I +mr22)2 2 = 1(I +mr12)/(I + mr22) 2 = 7.7 rad/s

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