In the figure the lower disk, of mass 460 g and radius 3.3 cm , is rotating at 1

Question

In the figure the lower disk, of mass 460 g and radius 3.3 cm , is rotating at 180 rpm on a frictionless shaft of negligible radius. The upper disk, of mass 280 g and radius 2.3 cm , is initially not rotating. It drops freely down onto the lower disk, and frictional forces bring the two disks to a common rotational speed. (Figure 1) Part A Find the common speed. Express your answer using two significant figures. f = rpm SubmitMy AnswersGive Up Part B Find the fraction of the initial kinetic energy lost to friction. Express your answer using two significant figures.

Explanation / Answer

angular momentum about axle will be conserved

(460 (3.3^2 ) /2) (180) = (460 (3.3^2 ) /2 +280 * (2.3^2) /2)) w

w = 138.922749823 rpm

fractional lost kE = ( 0.5*((460 (3.3^2 ) /2 +280 * (2.3^2) /2))) (138.922749823)^2 - 0.5 ((460 (3.3^2 ) /2) (180^2))/(0.5 ((460 (3.3^2 ) /2) (180^2)))

= 0.22820694542

=0.23

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