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ziro4ka [17]
3 years ago
8

A disk rotates freely on a vertical axis with an angular velocity of 30 rpm. An identical disk rotates above it in the same dire

ction about the same axis, but without touching the lower disk, at 20 rpm. The upper disk then drops onto the lower disk. After a short time, because of friction, they rotate together. The final angular velocity of the disks is
A. 50 rpm
B. 40 rpm
C. 25 rpm
D. 20 rpm
E. 10 rpm
Physics
1 answer:
weqwewe [10]3 years ago
8 0

Answer:

c. 25 rpm

Explanation:

The inertia of both disk is the same so

I_1=I_2

I_1*w_{1i}+I_2*w_{2i}=I_1*w_{1f}+I_2*w_{2f}

I*(w_{1i}+w_{2i})=I*(w_{1f}+w_{2f})

w_{1f}=w_{2f}=w_f

w_{1f}+w_{2f}=2w_f

w_f=\frac{w_{1i}+w_{i2}}{2}

w_f=\frac{30rpm+20rpm}{2}

w_f=\frac{50rpm}{2}

w_f=25rpm

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