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Homework Help: Angular impulse

  1. Apr 16, 2014 #1
    1. The problem statement, all variables and given/known data
    A thin rod of length L, mass m is suspended horizontally at rest. It is suddenly released and experiences immediately after an impulse vertically upwards at one end.

    I need to find the maximum height reached by the centre of mass and the angular velocity of rotation about the centre of mass.

    3. The attempt at a solution
    I can't see how there is enough information given in the question. I have used the fact that J=0.5Lp here (J is angular momentum) from the relation between angular and linear impulse, and then this means 0.5Lmv=Iω, with I=mL2/12. Then 0.5Lmv=mL2ω/12. This relates v and ω by v=ωL/6. I could then probably work with constant acceleration formulae to get the answer, however both v and ω are unknowns (and I have to find ω in the next part) so I have no idea where to go.

    Thanks in advance :)
  2. jcsd
  3. Apr 16, 2014 #2
    The initial velocity of CM ,angular velocity of the rod and the maximum height reached all depend upon the magnitude of impulse . So surely some data is missing from the question.
  4. Apr 16, 2014 #3
    Yes, as I suspected. Thanks for clarifying.
  5. Apr 16, 2014 #4


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    Well to me it looks as thought OP isn't supposed to solve for a number, but max height as a function of I.
  6. Apr 16, 2014 #5


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    Length L, mass M, impulse, I...
  7. Apr 16, 2014 #6


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    Except that no label is given for the impulse in the question as stated in the OP - that's what's missing.
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