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Sliding down a sliding plane

  1. Dec 5, 2009 #1
    1. The problem statement, all variables and given/known data

    A point particle of mass m is sliding down a wedge inclined at an angle of [tex]\alpha[/tex] to the horizontal. The wedge has a mass m and is free to slide on a smooth horizontal surface. When the mass has fallen a height h, what will be the speed of the wedge?

    2. Relevant equations



    3. The attempt at a solution

    I tried a kinematics approach with a lot of angle-bashing and eventually came up with:

    [tex]v = \frac{h}{g^2} \cot \alpha[/tex]

    But this is wrong, and I have a feeling this is too complex for kinematics

    I've thought about a conservation of energy approach with

    [tex]mgh = \frac{1}{2}mu^2+\frac{1}{2}mv^2[/tex]

    where 'u' is the speed of the particle and 'v' is the speed of the block, but I don't know how to divde up the speeds!

    thanks
     
  2. jcsd
  3. Dec 5, 2009 #2

    ideasrule

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    Homework Helper

    Have you tried the conservation of momentum? There's no external forces in the x direction, so horizontal momentum must be conserved.
     
  4. Dec 5, 2009 #3
    Thanks, I hadn't considered conservation of momentum, I think i've got it now
     
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