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Homework Help: Can someone please check this modified pendulum velocity problem

  1. Dec 22, 2009 #1
    [solved] Can someone please check this modified pendulum velocity problem

    1. The problem statement, all variables and given/known data
    I'm looking for the ballistic pendulum velocity for a simple machine (pull back lever, it shoots a marble into a block that raises to a certain degree measured)

    I have the angle that the block is raised
    length of the string
    mass of block

    2. Relevant equations
    Ke=Pe (1/2MV^2=MGH)
    cos@=length of sting - height/length of string

    3. The attempt at a solution

    .20cos25.3 = .20 - h

    which gives me .02cm, which in turn gives me .6m/s, which seems a bit slow, I feel as if I'm messing up my trig but I don't know where...


    I figured out I was using an incorrect derivation, I was just so fixed on thinking I had messed up my trig work
    Last edited: Dec 22, 2009
  2. jcsd
  3. Dec 22, 2009 #2
    I'm confused in what you want us to check? What specific quantity are you concerned about?

    The intial velocity of the object after its pulled back a certain distance?
  4. Dec 22, 2009 #3
    I've been given the manufacturers velocity, which is 5.5m/s, I'm getting less than 1m/s and honestly I don't see what I'm doing wrong.
    BTW here is the pendulum I used:
  5. Dec 22, 2009 #4
    What exactly is this:

    V = Rad(9.8 * 0.2)/0.5

  6. Dec 22, 2009 #5

    masses cancel, divide both sides by .5
    take the square root of both sides to get v=rad(GH)/.5
  7. Dec 22, 2009 #6
    Just your notation--rad is confused with radians. [tex]\sqrt{}[/tex] is available on the latex option on advanced setting with the icon:[tex]\Sigma[/tex] Or simply denote as sqrt(gh/.5)
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