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1. The problem statement, all variables and given/known data

Object: a disk-shaped grindstone of mass 1.69 kg and radius 7.95 cm that operates at 707 rev/min. When the power is shut off, you time the grindstone and find it takes 32.1 s for it to stop rotating. What is the angular acceleration of the grindstone? (Assume constant angular acceleration.)

2. Relevant equations

W=.5mv^2

V=distance/t

W=Wo+at

a=alpha, which is angular acceleration

3. The attempt at a solution

V=[707*(2pi/60)]/32.1 =2.31m/s

W=0

Wo=.5(1.69)(4.50^2) =4.50J

0=4.50+a(32.1)

therefore,a=-.140 rad/s^2

however, this is the wrong answer according to the program. It didn't have a problem with the units though, so I don't know what I am doing wrong. Please point out any wrong assumptions or completely wrong or silly mistakes. THANK YOU!

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# Homework Help: Grindstone angular acceleration

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