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jhwatts
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Homework Statement
2 metal disks, one with radius R1= 2.5cm and mass M1=.8kg and the other with radius R2=5.00cm and mass M2=1.60kg, are welded together and mounted on a frictionless axis through their common center.
a)What is the total moment of inertia of the two disks?
b)A light string is wrapped around the edge of the small disk, and a 1.5kg block, suspended from the free end of the string. If the blook is 2.00m above the floor what is the speed of just before it strikes the floor?
Homework Equations
I = Σ mi *ri^2
K = 1/2 *I*ω^2
W(g)= m*g*h
The Attempt at a Solution
a) I = 0.8kg*(2.5cm)^2 +1.6kg(5.00cm)^2 = 45kg*cm = .0045kg*m
b) m*g*h = 1/2 *I*ω^2
i) 1.5kg*9.8m/s^2*2m = .5*(.0045kg*m) * ω^2
ii) ω = sqrt[(1.5kg*9.8m/s^2*2m ) / (.5*(.0045kg*m))]
This is what i thought i should do, but looking at the solution in the back of the book, i doesn't seem to be correct. Any help is appericated, thanks.
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