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Homework Help: Shm help

  1. Dec 6, 2006 #1
    1. The problem statement, all variables and given/known data

    Astronauts in space cannot weigh themselves by standing on a bathroom scale. Instead, they determine their mass by oscillating on a large spring. Suppose an astronaut attaches one end of a large spring to her belt and the other end to a hook on the wall of the space capsule. A fellow astronaut then pulls her away from the wall and releases her. The spring's length as a function of time is shown in the figure.
    http://session.masteringphysics.com/problemAsset/1001073/9/knight_Figure_14_36.jpg

    What is her speed when the spring's length is 1.2 ?


    2. Relevant equations



    3. The attempt at a solution

    i tried to write the position as x(t)= .6+1.4sin((2pi/T)t)
     
  2. jcsd
  3. Dec 6, 2006 #2

    berkeman

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    Staff: Mentor

    The center of the sine wave is at 1.0m, not at 0.6m

    Re-write the position equation with a number for T, then differentiate and figure out what phase to plug into the velocity equation. You're good to go!
     
  4. Dec 6, 2006 #3

    nrqed

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    Yes...Keep going. To find the speed you have to differentiate your equation, find the time corresponding to a position of 1.2 , plug that time in your equation for the velocity and get your answer. (you may read the period T from your figure)

    Patrick

    EDIT: I just noticed on the figure that the oscillation is from 0.6 to 1.4, so the equation should be [itex] 1+ 0.4 sin ({2 \pi \over T} t ) [/itex]
     
    Last edited: Dec 6, 2006
  5. Dec 6, 2006 #4
    so i should differentiate [itex] 1+ 0.4 sin ({2 \pi \over T} t ) [/itex]
    for t and Tshould be 3??
     
  6. Dec 7, 2006 #5

    berkeman

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    Staff: Mentor

    Yep, that's the next step.
     
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