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Energy question

  1. Nov 11, 2008 #1
    1. The problem statement, all variables and given/known data

    Hey guys.
    So I got this disk connected to a spring which is connected to a wall.
    A mass m hits the disk with a velocity v and sticks to it.
    The question is to find the velocity of m at point A.
    As you can see I used the conservation of the angular momentum to find [tex]\omega[/tex] at the beginning.
    The thing I'm not sure about is the energy conservation equation I wrote there, I'm not sure about the gravitational potential energy, I mean, is this right?


    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Nov 11, 2008 #2
    Any idea guys?
  4. Nov 11, 2008 #3


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    Gold Member

    I'm not sure I fully understand the diagram, but shouldn't v*cos(squiggle)=0?
  5. Nov 11, 2008 #4
  6. Nov 11, 2008 #5


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    Gold Member

    That's why I posted that I didn't understand the diagram.
    Is the disk resting on the floor at y=0?
    Is the disk pivoted frictionlessly at it's center?

    I assumed that since you mentioned gravity, that the disk is in a vertical plane.

    My assumption was that the disc was fixed on some axis or point and therefore the v*cos(squiggle) component had to be zero. Also, none of the momentum of the mass m would be imparted to the disc as there was no mention of it's mass. So the magnitude of of the velocity of mass m would have to be the same in the direction of sin(squiggle).

    Hope that helps.
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