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Energy and motion problem

  1. Apr 6, 2010 #1
    1. The problem statement, all variables and given/known data
    Betty weighs 427 N and she is sitting on
    a playground swing seat that hangs 0.22 m
    above the ground. Tom pulls the swing back
    and releases it when the seat is 0.88 m above
    the ground.
    The acceleration of gravity is 9.8 m/s2 .
    How fast is Betty moving when the swing
    passes through its lowest position?
    Answer in units of m/s.


    2. Relevant equations
    KE=1/2 M V^2
    PEg=Mgh
    i might be missing an equation here


    3. The attempt at a solution
    i was thinking that potential energy gravitational would turn into Kinetic energy then i solved for v.

    PEg= 427 newtons*.66 i used the change in height for h and got 281.82 Joules for my answer. then i said that should transfer to KE.

    281.82 joules= 1/2* 427/9.8 Kg * V^2 and i got 11.3737 m/s as my answer. when i checked this it turned out to be wrong. i think i may have to apply circular motion concepts to this problem, but i'm not quite sure how to do that.

    thanks in advance.
     
    Last edited: Apr 6, 2010
  2. jcsd
  3. Apr 6, 2010 #2
    Your logic looks sound; it must just be a math error throwing you off... If the work you have here is what you typed into your calculator, then I have two suggestions: first, the weight in the 2nd equation should be 427, not 527... secondly, did you take the square root of both sides at the end? Other than that, I don't know what to tell you.
     
  4. Apr 6, 2010 #3
    yeah i've got it figured out now thanks.
     
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