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Math Help - Parachutist landing on a turntable

  1. #1
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    Parachutist landing on a turntable

    A turntable in the shape of a flat uniform disk has a radius of 2m and a total mass of 120kg. The turntable is rotating at 3rad/s about a verticla axis through its centre. Suddenly a 70kg parachutist lands on the outer edge.(model parachutist as a particle. Find the angular speed of the turntable after the parachutist lands.

    My working so far:
    I_a \omega_a = I_a_b \omega_a_b
    \frac{1}{2}\times120\times2^2\times3 = [(\frac{1}{2}\times120\times2^2\times3) + (70\times2^2)]\omega_a_b
    \omega_a_b = \frac{720}{1000}
    \omega_a_b = 0.72

    however my textbook says 1.38 rad/s???????
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  2. #2
    MHF Contributor
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    A turntable in the shape of a flat uniform disk has a radius of 2m and a total mass of 120kg. The turntable is rotating at 3rad/s about a verticla axis through its centre. Suddenly a 70kg parachutist lands on the outer edge.
    Happens all the time

    \frac{1}{2}\times120\times2^2\times3 = [(\frac{1}{2}\times120\times2^2\mathbf{\times3}) + (70\times2^2)]\omega_a_b
    There should not be \times3 shown in bold above.
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  3. #3
    A Plied Mathematician
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    Reply to emakarov:

    Hey. Didn't know you even peeked at the Advanced Applied Math forum!
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