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Amount of time for a half period to occur

  1. Oct 25, 2011 #1
    1. The problem statement, all variables and given/known data

    A mass-spring system has k = 105 N/m and m = 1.75 kg.

    If it is undergoing simple harmonic motion, how much time does it take the mass to go from x = A to x = 0?

    2. Relevant equations

    T=2pi*sqrt(m/k)

    3. The attempt at a solution

    Tried plugging in the values for the equation I gave to find T, then cutting it in half to find the amount of time the question asked for, but it's not the correct answer.
     
  2. jcsd
  3. Oct 25, 2011 #2

    vela

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    What exactly is one cycle? If you understand that, you'll see why your answer is wrong. It may help to look at a diagram that shows one period in your textbook.
     
  4. Oct 25, 2011 #3
    When the mass goes into the spring and back?
     
  5. Oct 25, 2011 #4

    ehild

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    Sketch the x(t) function for a full period and see.

    ehild
     
  6. Oct 25, 2011 #5

    vela

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    Yes. So in one cycle, if it starts at x(0)=A, it ends at x(T)=A, but more important, what does x(t) do in between? As ehild suggested, plot x(t) for one cycle.
     
  7. Oct 25, 2011 #6

    dextercioby

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    Who's A and can you link it to T ? EDIT: So A's the amplitude...
     
    Last edited: Oct 26, 2011
  8. Oct 25, 2011 #7
    Uhh x goes to A? Which equation can I use to solve for that? x=Acos(ωt)?

    Sorry I'm braindead been studying all morning I just want this homework done.
     
  9. Oct 25, 2011 #8

    ehild

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    Yes. x = A cos (2pi* t/T). How does it look like? What is x at t=0, t=T/8, T/4, ...

    ehild
     
  10. Oct 25, 2011 #9
    So I can plug in x as A so that A cancels out here and then solve for t where T = 1/2?
     
  11. Oct 26, 2011 #10

    ehild

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    Is T=1/2???????


    Would you please show me a cosine function? Please!!!!

    ehild
     
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