- #1

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[tex] L_o= L_f [/tex]

[tex] (1/2)MR^2 * \omega = (MR^2)(\omega) [/tex]

[tex] (1/2) (81.1)(3.43^2) = (56.3)(1.67^2)(\omega) [/tex]

Solving for omega gave me 6.1 rad/s which wasn't right.

Can someone help me?

- Thread starter Punchlinegirl
- Start date

- #1

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[tex] L_o= L_f [/tex]

[tex] (1/2)MR^2 * \omega = (MR^2)(\omega) [/tex]

[tex] (1/2) (81.1)(3.43^2) = (56.3)(1.67^2)(\omega) [/tex]

Solving for omega gave me 6.1 rad/s which wasn't right.

Can someone help me?

- #2

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- #3

Astronuc

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Science Advisor

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The disc has moment of inertia 1/2mr

See this discussion for a composite system and superposition of moments of inertia - http://hyperphysics.phy-astr.gsu.edu/hbase/tdisc.html#icomp

Assume conservation of angular momentum applies as you did.

- #4

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[tex] L_o= (1/2)MR^2 + MR^2 * \omega[/tex]

[tex] (1/2)(81.1)(3.43^2) +(56.3)(3.43^2) *4.90 [/tex]

[tex] L_o= 3284 [/tex]

[tex] L_f= (1/2)MR^2 + MR^2 *\omega[/tex]

[tex] (1/2)(81.1)(3.43^2) +(56.3)(1.67^2) *\omega[/tex]

Solving for omega gave me 5.04 rad/s, which isn't right...

- #5

Astronuc

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Science Advisor

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Try

[tex] L_o= ((1/2)MR^2 + MR^2) * \omega[/tex]

Remember L = I x [itex]\omega[/itex] and I = [itex]\Sigma_i\,I_i[/itex].

- #6

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Wow I feel dumb :rofl:

Thanks

Thanks

- #7

Astronuc

Staff Emeritus

Science Advisor

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Don't feel dumb - just be careful.

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