0.341 points I Previous Answers Tipler6 10.P049.soln. u stand on a frictional pl

Question

0.341 points I Previous Answers Tipler6 10.P049.soln. u stand on a frictional platform that is rotating Your arms are outstretched, and you hold a at 1.6 rev/s. pull the weights in toward your body, the moment of inertia decreases 4.8 kg m2. to (a) what is the resulting angular speed of the platform? rev/s (b) what is the change in kinetic energy of the system? (c) Where did this increase in energy come from? (Select all that apply.) air resistance kinetic energy of the platform mass of the weights gravity your internal energy Interactive Example eBook

Explanation / Answer

Using law of conservation of angular momentum

Li = Lf

I1*w1 = I2*w2

9*1.6 = 4.8*w2

w2 = (9*1.6)/4.8 = 3 rev/sec = 3*2*3.142 = 18.852 rad/s

w1 = 1.6 rev/sec = 1.6*2*3.142 = 10.05 rad/sec

b) chnage in kinetic energy is Kf - ki = (0.5*I2*w2^2)-(0.5*I1*w1^2)

Kf-Ki = (0.5*9*10.05^2)-(0.5*4.8*18.852^2) = -398.45 J

c) lost in kinetic energy appeared as internal energy

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