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Homework Help: Simple Harmonic Motion of a gun

  1. Mar 25, 2008 #1
    (1)It takes a force of 75 N to compress the spring of a toy popgun 0.18 m to "load" a 0.14 kg ball. With what speed will the ball leave the gun?

    I used the equation F=kx
    I solved for K and I got 416 N/m

    Then I used the equation omega = square root(K/M)
    I solved for omega and i got 54.5.

    Is this correct? It seems wrong to me. Please help, any suggestions will be greatly appreciated.
    Last edited: Mar 25, 2008
  2. jcsd
  3. Mar 26, 2008 #2
    Hint: This is not a S.H.M. problem.
    f= -k*x
    k>> 416 N/m
    This is not necessary.
  4. Mar 26, 2008 #3
    The spring energy is converted into kinetic energy. Do you know what the spring energy is now that you know K? Can you figure out the velocity with this?
  5. Mar 26, 2008 #4
    Thank you both for your help. I'm still not sure if I completely understand this problem

    PE= 1/2kx^2
    where I know k because it is 416 N/M and X=.18. so I would solve for the PE.

    Then you're saying if the spring energy is converted to kinetic energy, then is KE=PE?
    thus KE= 1/2mv^2 and then I would have to solve for v?

    But I still don't think this is right because where is the 75N coming in?
  6. Mar 26, 2008 #5
    You used it to find K, did you not?
  7. Mar 26, 2008 #6
    Yeah, I'm an idiot. Thanks for your help.
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