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Rotating rigid body

  1. Jun 14, 2017 #1
    1. The problem statement, all variables and given/known data

    Two masses of 2 kg are attached to the extremities of a 5 cm long, negligible mass and thin bar, free to rotate around a horizontal axis passing through its center. A drop of wax falls on one of the two masses at ##v = 3 \frac{m}{s}## and sticks to it. Retrieve the angular velocity of the system immediately after the impact

    2. Relevant equations

    Angular moment:
    $$ L = I \cdot \omega $$
    $$ L = rp = rmv $$
    Inertia moment:
    $$ I = (M + M + m) \cdot r^2 $$

    3. The attempt at a solution

    I don't know if the wax drop mass was deliberately omitted in the text, but if so, how can I get it? Without that I can not get ## \omega ##. I know I should do some attempt, but the only thing that comes to mind is the inertia moment for a thin bar

    $$ I_{MC} = \frac{1}{12} m \cdot l^{2} $$

    Can you help me? Thanks in advance
  2. jcsd
  3. Jun 14, 2017 #2

    Doc Al

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    Staff: Mentor

    You'll need the mass of the wax drop to solve this. Where did you get the problem?
  4. Jun 14, 2017 #3
    An italian homework book. Indeed the latest edition dates back to 2003
  5. Jun 14, 2017 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Oh well. Without the mass the best you can do is solve things in terms of 'm', but that's clearly not the intention since quantities are given for everything else.
  6. Jun 14, 2017 #5
    Thank you! You have confirmed that I understand the subject well :D
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