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Posted by on Saturday, November 19, 2011 at 12:20pm.

Two disks of identical mass but different radii (r and 2r) are spinning on frictionless bearings at the same angular speed ω0, but in opposite directions. The two disks are brought slowly together. The resulting frictional force between the surfaces eventually brings them to a common angular velocity.


(a) What is the magnitude of that final angular velocity in terms of ω0? (Use the following as necessary: ω0.)

(b) What is the change in rotational kinetic energy of the system? (Use the following as necessary: K as the initial kinetic energy.)
Explain.

  • Physics - , Saturday, November 19, 2011 at 12:23pm

    Conservation of rotational momentum applies.

    I1*w1+I2*w2= (I1+I2)wf

    you know w2=-w1=wo
    I1=k*mr1^2
    I2=k*mr2^2

    Solve for wf, it is just algebra.

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