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Energy of motion

  1. Feb 23, 2009 #1
    1. The problem statement, all variables and given/known data
    A 2.4kg- mass attached to a spring oscillates with an amplitude of 7.0cm and a frequency of 5.0Hz .
    What is its energy of motion?
    Express your answer using two significant figures.
    in J.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 23, 2009 #2
    people are gonna ask you to give it a shot be for they help. Lets start with what equations should you use>
  4. Feb 23, 2009 #3


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    Homework Helper

    You have two energy formulas that apply:
    E = 1/2*k*x^2 for when the spring is stretched but the bob is not moving.
    E = 1/2*m*v^2 when the object is moving but the spring is not stretched.
    Looks like the first one will be easier to work out!
  5. Feb 23, 2009 #4
    ok i have my T which is 0.2s
    omega is 31.4
    k is 2366.3
    and amplitude is 7
    eqn to be used is E=1\2kA(squared) i believe but i cannot get the correct answer doing so
  6. Feb 23, 2009 #5


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    Homework Helper

    I haven't seen E = 1/2*k*x^2 written with an A instead of an x.
    The x means "extension" or how much the spring is stretched.
    Or compressed.
    That just means the 7 cm, I think.

    As the spring oscillates, this energy is repeatedly converted back and forth between spring energy and kinetic energy. If you knew the maximum speed of the bob, you could use E = 1/2mv^2 and get the same answer. Or you could set 1/2*k*x^2 at maximum extension equal to 1/2mv^2 at maximum speed and solve for the speed.
  7. Feb 23, 2009 #6
    i see, i still cannot get the right answer i dont no waht im doing wrong
  8. Feb 23, 2009 #7
    my answers come to 580 or 5.8*10^5
    and it comes up wrong
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