Homework Help: Physics

Posted by Mary on Tuesday, March 13, 2007 at 2:41pm.

A certain CD has a playing time of 80 minutes. When the music starts, the CD is rotating at an angular speed of 4.8 102 revolutions per minute (rpm). At the end of the music, the CD is rotating at 2.1 102 rpm. Find the magnitude of the average angular acceleration of the CD. Express your answer in rad/s2.

avgangularacceleration= (wf-wi)/time

change rpm to rad/sec (rpm*2PI/60)

please tell me where i went wrong.

(2.1x10^2rpm - 4.8x10^2rpm)/ 80mins

(-270rpm)/ 80mins

change rpm to rad/sec

rpmx2(3.14)/60

(-270 rpm x 6.28)/ 60 = -28.26 rad/s

-28.26rad per sec / 80x60

av ang acc = -0.0058875

where you went wrong?
Looks right to me, except for the sig figures.

avg ang acc= (wf-wi)/t=2PI/60 *(2.1
E2-4.8E2)/80*60= 5.9E-3 rad/sec^2

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